Inside Double-D Washers - Anti-Rotation Specialty Flat Washers

Inside Double-D Washer Frequently Asked Questions

Below are answers to some of the most common questions about inside double-D washers.

What are inside double-D washers?
Inside double-D washers feature two parallel flat edges on the inner diameter, creating a double-D (or parallel flat) bore that mates with double-D shafts and fasteners. This geometry provides positive anti-rotation engagement on both sides of the shaft, offering stronger and more symmetrical locking than a single-D bore. Superior Washer stocks 6 inside double-D configurations in two ID sizes (0.190" and 0.376") and two thickness options (0.030" and 0.060").

What is the difference between inside D-shaped and inside double-D washers?
An inside D-shaped washer has one flat edge on the bore, engaging one flat surface of a D-profile shaft. An inside double-D washer has two opposing flat edges, engaging both flat surfaces of a double-D (parallel flat) shaft. Double-D provides more secure anti-rotation performance and is used where the single-D configuration cannot fully prevent indexing or where higher torque resistance is required.

What applications use inside double-D washers?
Inside double-D washers are used in drive shafts, power tools, electric motors, actuators, and precision mechanical assemblies where a double-D shaft profile is specified for positive rotational locking. They are common in automotive, industrial, and consumer product applications requiring reliable shaft engagement.

What materials are inside double-D washers available in?
Inside double-D washers are produced in steel, stainless steel, brass, and aluminum. Contact us to specify the material required for your application.

Can you produce custom inside double-D washers?
Yes. If the 6 stocked configurations do not meet your dimensional requirements, we manufacture custom inside double-D washers to your ID, OD, thickness, and flat-to-flat specifications. Contact us via the Quick Quote form or call NY (631) 273-8282 or SC (803) 366-3250.

Are your inside double-D washers made in the USA?
Yes. All inside double-D washers are manufactured in the United States under our ISO 9001:2015 certified Quality Management System at our Hauppauge, NY and Rock Hill, SC facilities.

Need a single-D bore or a different odd shape instead? Browse the full flat washers catalog to see all shapes and materials available.