Stock Drive Products/Sterling Instrument (SDP/SI)

Highest quality mechanical products and engineered mechatronics solutions an services. Offering the world’s most complete standard one stop shop for small and miniature mechanical components, comprehensive global supply and distribution, and high precision customized assemblies.

SDP/SI – Quality Management System


Stock Drive products and Sterling instrument are AS9100C certified. Providing custom and standard mechanical components serving the aerospace industry.



SI is Boeing certified supplier






ITAR – Tnternational Traffic in Arms Regulation

DDTC – Directorate of Defense Trade Controls



RoHS: Restriction on use of Hazardous Substances




REACH: Registration, Evaluation, Authorisation and Restriction of chemicals






Stock Drive Products/Sterling Instrument (SDP/SI) practices the principle of lean manufacturing. Lean is centred on preserving value with less work.Lean is production practice that considers the expenditure of resources for any goal other than the creation of value for the end customer to be wasteful and thus a target of eveluation

Shaftloc® – A Superior Way to Fasten Rotating Components

Shaftloc® is a registered trademark of Stock Drive Products/Sterling Instrument

Shaftloc® is a patented fastening system that makes use of a simple two-piece construction to secure rotating components to a shaft. The key to this compact, efficient design is the wedging action created by its unique thread profile. Full details on this design and its advantages are given in the catalog. Several styles of Shaftloc® fastener are available, as well as special pulleys to be used with them.

Fairloc® – The Integral Fastener

Fairloc® is a registered trademark of Stock Drive Products/Sterling Instrument

Fairloc® is the better way to fasten rotating components. It solves phasing, timing, positioning and frequent removal problems.

  • Easy Adjustment: Fairloc® replaces set screws and clamps; components can be repositioned with a single hex key adjustment.
  • Will not Mar Shaft
  • Outstanding Reliability
  • Compact, Self-Contained Design: When available space or access is limited Fairloc’s® small hub envelope is a distinct advantage.
  • Full Use of the Bore: Gives maximum support to the component, reduces wobble or misalignment.
  • Superior to Other Fasteners in High-Torque

SDP/SI – Gears

SDP/SI is a well-known manufacturer of high precision custom gears for a wide range of applications, including but not limited to the aerospace, defense and medical industries. In addition to our custom capabilities, we offer hundreds of cost effective, off-the-shelf standard gears which are available in metal and plastic materials. Many of our stock gears are available or can be made with the superior Fairloc® hub design.
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SDP/SI — Timing Belts & Pulleys

SDP/SI, is known as the go-to source for synchronous drive components. We have built a reputation among designers of small mechanisms and drives for providing quality, inch and metric timing belts and timing belt pulleys. We stock a large selection of standard sizes as well as hard-to-find components for both custom and standard applications at competitive prices.

For 50 years we have been providing our clients with pulley systems and components in small to large quantities, including OEM’s. Individual service, flexible stocking plans, customization and J.I.T. delivery are some of the benefits you receive when working with SDP/SI.

Center Distance Designer:

SDP/SI & QBC — Bearings & Bearing Maintenance Equipment

SDP/SI bearingsWe maintain a large inventory of precision and commercial quality ball bearings, thrust bearings, needle roller bearings, linear and sleeve bearings, and linear systems.
Ball Bearings: ABEC Tolerance 1, 3, 5, and 7 are available in a variety of types and with the lubricant to fit your application.
Plain or Flanged Pressbearings: Feature a self-aligning bore up to 5° and are self-lubricating.
Needle Roller Bearings and Needle Roller Clutches: Our shell-type needle roller bearings handle high-speed applications and the needle roller clutches are ideal for indexing, backstopping and overrunning applications.
Sleeve Bearings: A wide selection of nonmetallic, self-lubricating split-type, ultra precision, and small and standard series in sintered bronze is available.
Linear Bearings: Frelon® lined bearings, precision shafting and guide blocks.
Spherical Bearings and Rod Ends: Precision and commercial types.
Thrust Bearings & Washers
Pillow Block and Flange Mounted Bearings: Miniature and wash-down styles.

Aditional products available from QBC.
Thomson Linear Motion Components

Machine breakdowns are frequently caused by bearing damage. Unplanned downtime, as well as unnecessary repair work, can be significantly reduced by periodically checking bearing condition. QBC offers a wide range of high-quality induction heaters for sale and efficient use in industrial applications. The sturdy and user-friendly design guarantees years of problem-free operation.

Bearing Induction Heaters
Bearing Monitoring Tools
Hydraulic & Mechanical Pullers
Alignment Equipment

SDP/SI — Clutches & Brakes

SDP/SI offers a wide selection of quality clutches and brakes that are immediately available off-the-shelf. We can also re-engineer or modify these products to fit your exact requirements. Not only do we provide a vast collection of components, but we also build fully integrated systems from these components to your specifications.

Our Line of Clutches and Brakes Includes

Mechanical Slip Clutches: provide very low backlash, overload protection and torque control. Miniature sizes are also available for small space requirements.
Spring Wrapped Clutches and Brakes: provide start-stop, overrunning and single revolution functions.
Electromagnetic Clutches and Zero-backlash Clutch Couplings: provide very fast response and friction-free operation. They’re ideal for applications such as printers, packaging and office automation.
Power-on and Power-off Electromagnetic Brakes: provide switchable means of stopping and /or holding a load.
Hysteresis Brakes and Clutches: provide smooth, stable, noise-free operation. They are infinitely adjustable and maintenance free. Special mounting configurations and modified shafts are available.
Power-Off Servo Brakes: economical choice that are energy efficient and are easy to install.
Magnetic Particle Clutches and Brakes: provide ultrafast response, silent and smooth operation and no backlash.
Reverse-Acting Brakes: BuOrd Size 11, 18
Clutches & Clutch Brakes: BuOrd Size 18
Reverse-Acting Brakes: BuOrd Size 18

Complete engineering and technical assistance is available by contacting our Engineering Department. If you would like to receive pricing information for your application, select the link to our Product Inquiry Form.

SDP/SI — Right Angle Gear Drives

SDP/SI provides a wide selection of miniature to small right angle gear drives. Available off-the-shelf: inch and metric sizes, low backlash and ratios of 1:1 to 100:1. Modifications or custom designs can be produced if the standard does not meet your application requirements.

Our Line of Right Angle Gear Drives Include:

Miniature Right Angle Bevel Gearboxes: 1:1 Ratio, Low Backlash, Torque from 2 to 70 ozf in.
Right Angle Bevel Gear Drives: 1:1 to 3:1 Ratio, rated speeds up to 1800 rpm
Right Angle Bevel Gear Drives: Precision Quality, 1:1 Ratio, input speeds up to 3000 rpm
Heavy-Duty Bevel Gear Drives: “L” and “T” design, 1:1 to 2:1 Ratio, low noise and high efficiency, easy to install, reversible.
Low-Cost Right Angle Bevel Gear Drives: 1:1 to 2:1 Ratio, rated speeds up to 500 rpm
Worm Gear Speed Reducers: Commercial Quality, 3.5:1 to 100:1 Ratio
Miniature Right Angle Worm Gear Drives: 5:1 to 20:1 Ratio, 200 ozf in. output Torque
Miniature Right Angle Bevel Gear Drives: 1:1 to 3:1 Ratio, 200 ozf in. output Torque
Worm Gear Speed Reducers: Precision Quality, 6:1 to 100:1 Ratio, High Torque, 6000 rpm Input Speed
Right Angle Helical Gear Speed Reducers: 1:1 to 25:1 Ratio, Base or Panel Mounted Design
Right Angle and Dual Helical Gear Drives: 1:1 Ratio, Light or Heavy Duty Type
Miniature Right Angle Helical Gear Drives: 1:1 to 2:1 Ratio, Lightweight, Base or Panel Mounted Design
Right Angle Helical Gear Drives: 1:1 to 1.5:1 Ratio, Built-in Keyway, simply add keyed shafting, right- or left-hand shaft rotation.

Custom Design Gearheads and Speed Reducers

Many applications require a custom unit. Below is a list of some of the special applications gearheads and speed reducers that Sterling Instrument can produce from their inventory of existing designs.
Zero-Backlash Gearheads and Speed Reducers: For applications which require minimal lost motion throughout the gear train.
Splined Shaft Gearheads and Speed Reducers: For applications which require direct meshing with other component parts of the gear train.
Low-Backlash Gearheads and Speed Reducers: For applications which do not require zero backlash, but do require lower backlash than our standard units.
Tandem Gearheads and Speed Reducers: For applications which require reduction ratios higher than shown for our standard units.
Exact Ratio Gearheads and Speed Reducers: For applications requiring reduction ratios which are even integers.
Integral Slip Clutch Gearheads and Speed Reducers: For applications which require a built-in torque limiting device.
Heavy-Duty Gearheads and Speed Reducers: For applications which require two or three times the available output torque of standard gearheads and speed reducers.


SDP/SI — Gearheads & Speed Reducers

SDP/SI provides a wide selection of ratios in both BuOrd (U.S. Bureau of Ordnance) and NEMA size gearheads and speed reducers to fit your application. We manufacture our gearheads and speed reducers to the highest exacting standards of craftsmanship.

The gearheads are attachable to BuOrd frame size servomotors without modifications to the input pinions and without complicated adapters. They are designed to be used in high-accuracy electromechanical systems. All gears are precision cut. The output gear and all stage pinions are made of hardened 416 Stainless Steel. Housings are black-anodized aluminum alloy and are precision bored for exacting center distances. The cantilever design combined with wide bearing span results in extremely low backlash.

Planetary gear and gearhead speed reducers that provide a high degree of position accuracy are also available. Our precision and economy planetary gearheads feature ratios from 3:1 to 700:1, standard NEMA sizes 17, 23, 34, and 42, inline, right angle and dual output styles. Spur gearheads, a low cost alternative to planetary gearheads are available in ratios from 3:1 to 100:1. If a standard unit design does not meet your expectations we can provide a custom design.

SDP/SI & QBC — Linear Motion Components & Systems

SDP/SI and QBC offers linear guide products and components that are suitable for automation and guided motion applications. A variety of styles are available off-the-shelf to meet specific load and speed requirements. Customization, individual service and J. I. T. delivery are a few of the services we provide our clients

Linear Motion Systems:

Industrial “V” Guide Systems are assembled from the following components: Guide Wheels, Track, Adapter Bushings, and Guide Wheel Journal Assemblies
• Easy to install and adjust
• Feature self-cleaning design
• Provide smooth and quiet operation
• High load and high speed capacity
• Low cost option available – Economy Series
Low Profile Linear Guide Systems are a great option when space is limited
• Small mounting height and width
• Low friction without lubrication
• Dirt and dust resistant
• Lightweight
• Low-cost alternative to miniature ball bearing systems
Mini-Rail® Linear Guides are self-lubricating, corrosion resistant and dampens vibration.
Rosa Sistemi Rolling Systems consist of Rails, Cages, Recirculating Linear Ball Bearings, Roller Tables, and Frictionless Tables
• Precise movement
• Lack of start-up frictional losses
• High load carrying capacity
• Minimum wear

Ball & Lead Screws:

Power screws are a common means of translating rotary motion into linear motion. There are several different types, each of which has its own advantages and disadvantages depending on the requirements of the application. Acme lead screws are defined by their thread profile, which is trapezoidal with a thread angle of 29°.

There are two immediate results of this difference in profile. It is much easier to machine, so Acme lead screws are much cheaper than square lead screws or ball screws. The second difference is a much larger area of contact between the screw and the nut. This has both advantages and disadvantages.

Universal Joints

A Universal Joint is a mechanical connection between two rotating shafts that intersect. We offer a wide selection of both metal and plastic universal joints in inch and metric sizes to fit your application.


Stock Drive Products pioneered the concept of combining selected plastic materials with different metals to create products which incorporate both; the result was SUPER-PLAST®. SUPER-PLAST® designs have the following advantages:

  • Inexpensive replacement of metal components, particularly for low torque applications
  • Dampens vibration due to the resiliency of plastics used
  • For drives used in corrosive environments or for chemical processing equipment
  • For drives which have to be electrically insulated
  • For intermittent duty applicationsSuperplast Universal Joints


Standard Universal Joints

Miniature Universal Joints: Single and Double Joint
Telescoping Miniature Universal Joints
Inverted Design Universal Joints:strong Single and Double Joint
Solid or Bored Universal Joints: Single Joint and Double Joint
Telescoping Universal Joints
Molded Universal Joints: Economy Series with or without molded slide extension
SUPERPLAST® Molded Universal Joints: Single or Double Joint, with or without molded slide extension
SUPERPLAST® Molded Universal Joints: Telescoping with brass slide extension

Custom Universal Joints

SDP molded universal joints are available from stock in standard configurations. They can also be manufactured to special requirements:

  • Bores can be molded to accommodate square, “D” shape or hexagonal shafts.
  • Shafts molded into the components themselves
  • Zero backlash or components with built-in backlash
  • Gears, pulleys or other components molded or assembled to couplings or universal joints

SDP/SI — Couplings & Shafts

Couplings are mechanical elements that allow motion transfer from one drive element (or shaft) to another. We offer thousands of different miniature to medium size couplings, available off-the-shelf, to meet your requirements. We can also produce custom couplings to meet your special application needs. Our patented Fairloc® hub design, available on many of our offerings, allows for fast and easy adjustment during assembly, significantly reducing setup time

Types of Couplings:

Bellows Couplings: Good misalignment capability and excellent torsional rigidity and torque capacity. Available with Fairloc® hub.
Flexible Couplings: Long Series Helical Couplings, Slit Type MSC Flexible Couplings and Slit Type Plastic Couplings. They provide excellent misalignment capability and good vibration damping.
Disc Couplings: Excellent torsional rigidity and torque capacity with good misalignment capability.
Precision Oldham Couplings & Standard Oldham Couplings: Good to excellent misalignment capability. The standard style features different bore combinations and are ease of assembly.
Jaw Couplings: High torque capacity with good vibration damping.
Rigid Shaft Couplings: High torque capacity and torsional rigidity. Available with our Fairloc® hub.
Magnetic Disk Couplings: Good misalignment capability and performance in high temperatures.
Neo-flex Couplings: Provides shaft-to-shaft insulation and torsional vibration isolation. Available with the Fairloc® hub
Precision Shaft Couplings: Made of 303 Stainless Steel. Can be ordered with other bore sizes to fit your specifications.

In addition to couplings, we offer flexible shafts:

Flexible Shafts are used in cases where a solid shaft is impractical, such as when there are obstacles in the way. The flexible shaft can be routed around, over and under the obstacle to fit your design. Off-the-shelf or made to your exact specifications, many combinations of fittings and lengths are available.

Couplings Selector:

QBC — Our Bearing Services

Ball Bearing Cleaning and Relubrication
Custom Packaging
Custom Bearings
Custom Design
JIT Deliveries and Blanket Orders
Purchasing of Excess Inventory
Hybrid Bearings
Cross Referencing Capabilities
Global Sourcing of Hard to Find Bearings

SDP/SI — Shafts & Shaft Accessories

SDP/SI manufacturers high quality components, including many types of precision shafting; specializing in the machining of components with tight tolerances that others can’t make. Our capabilities include Swiss machining, milling, tapping, and drilling in aluminum, steel alloys, stainless steel, and titanium. Custom packaging, labeling and J.I.T. deliveries are available.

Custom mechanical assemblies, using our precision shafting with gears, pulleys, bearings, and couplings from our product lines can be made for your application. For pricing information, go to our Product Inquiry Form.

SDP/SI — Chains & Sprockets

SDP/SI offers a full range of roller chains: standard and heavy-duty series, single and double stranded, molded and Stainless Steel; subminiature roller chain, miniature roller chain, and posi-drive belts with corresponding sprockets.

Sprockets, the smallest having 6 teeth, are shaft ready in a variety of bore sizes; offered in both plastic and metal. Also available is a wide selection of ladder chains and matching sprockets.

SDP/SI Design, Manufacturing Capabilities & Services

Manufacturing Designatronics. Call Underwood Sales to learn more. Gear Manufacturing Capabilities

Stock Drive Products/Sterling Instrument
Manufacturing CapabilitiesTurning: .25” – 6.0” ODMilling: maximum 12” x 20”

Gear Cutting:

Gears and Racks:
Inch: 16 DP to 200 DP
Metric: 2.0 m to 0.2 m
Worms and Worm Wheels: 16 DP to 72 DP

CNC Swiss Turning:
Multiple Splindle
CNC Lathe (Mill-Turn):
Multiple Spindle
CNC Milling & Machining Centers:
4-& 5-Axis
With AutomationGear Cutting:CNC Hobbing
CNC Shaping
Coniflex Bevel Gear Generators
Rack Cutting
Fully Equipped Tool Room:
Grinding Department
Deburring Department

100,000 Inch & Metric Mechanical Components:

Timing Belts and Pulleys
Commercial & Precision Gears
Precision Gearboxes
Shafting & Shaft Accessories
Couplings and Universal Joints
Linear Motion Systems
Gearheads & Speed Reducers
Right Angle Drives
Clutches & Brakes

Gear Tolerances:Molded Gears: to AGMA 5
Hobbed or Ground Gears: to AGMA 14Shafts:

Diameter: .03125” – 1.500”
Straightness: up to .0003”
Length: maximum 12’

Available Materials (abridged):

Alloy Steel
Stainless Steel

Compliances and Practices:

ISO 9001:2008 + AS9100C Certified
ITAR Compliant – DDTC Registered
RoHS Compliant
R.E.A.C.H. Compliant
ISO 7 Class 10000 Clean Room
Engineering Capabilities:
Reverse Engineering
Product Development
Over 170 Machines