Three collars fit around a standard screw.

While designing a new product, engineers at Frank Roth Co. Inc., Stratford, Conn., needed a fastener that didn't exist, so they invented one. Called the Uni-Key, the mechanical fastener can replace Woodruff keys, splines, and other methods for linking power transmission components. And, says Lou Toffolo, CEO, it can simplify keyway machining, eliminate hubs and setscrews on gears, sprockets, and pulleys, and make it easier to remove components from shaft ends.

Here's how it works. The Uni-Key has three collars that fit around a standard screw. The first collar is drilled to the screw size and fits like a washer. The second has an oversized center hole which lets it shift when the screw is tightened. The third collar is threaded to provide clamping force. Tightening the screw causes the three collars to move in opposing radial directions, forcing components together. The device's oblong shape prevents rotation in the mounting slot during installation. Because the Uni-Key expands to fit, tolerances for mounting slots can be relaxed, which saves machining costs. Mounting slots are made using a standard diameter ball end mill and a simple milling machine.

Another feature is its ability to be ganged. That is, instead of using a larger key to provide the necessary holding force, several smaller Uni-Keys can be used to handle larger torsional loads. This is useful when using shorter shafts and hubless gears.

The Uni-Key comes in four standard sizes ranging from 0.1 in. thick 3 0.25 in. long to 0.8 in. thick 3 2 in. long. Expansion ranges from 0.008 for the 0.1 size to 0.064 for the 0.8 size. It can also be used for electrical connectors and architectural structures. Free samples are available.

THICKNESS
S
WIDTH
T
OVERALL LENGTH
U
MAX EXPANSION
V
MODE SHAFT SIZE HOLDING TORQUE
lb-in
0.1 0.144 0.25 0.008 Friction
Shear
0.625 20
578
0.2 0.288 0.5 0.016 Friction
Shear
0.875 95
2,990
0.4 0.577 1 0.032 Friction
Shear
1.625 934
25,200
0.8 1.154 2 0.064 Friction
Shear
2.125 5,440
136,000
All dimensions in inches