ANSI B17.1 · square parallel keys

Keyway and keyseat dimensions

A keyseat is the slot milled into a shaft so a key can transmit torque to a hub. This is the ANSI B17.1 square-key schedule we cut to, sized by shaft diameter.

The key is a parallel bar that sits half in the shaft keyseat and half in the mating hub keyway, carrying torque between them in shear. For a given shaft diameter the standard fixes the key cross-section and the depth of the slot in the shaft; the numbers below are the square-key series, where the key width and height are equal.

Keyseat width is set by the key. Keyseat depth is how far the cutter goes into the shaft, and it is the dimension that decides how much shaft cross-section is left to carry bending. On a slender shaft a deep keyseat is often the failure point, which is why the material and the fit around it matter as much as the slot itself.

The depth column below is the cut depth the configurator uses for each key size. Enter a keyseat on any diameter and it lands on this schedule automatically; you set only the length and where along the shaft it sits.

Configure a part →

Square parallel keys and keyseats

Shaft Ø range (in)	Square key (in)	Keyseat width (in)	Keyseat depth (in)
0.3125 to 0.4375	3/32 sq	0.0938	0.0541
0.4375 to 0.5625	1/8 sq	0.125	0.0704
0.5625 to 0.875	3/16 sq	0.1875	0.1081
0.875 to 1.25	1/4 sq	0.25	0.142
1.25 to 1.375	5/16 sq	0.3125	0.1751
1.375 to 1.75	3/8 sq	0.375	0.2124
1.75 to 2.25	1/2 sq	0.5	0.2852
2.25 to 2.75	5/8 sq	0.625	0.3555
2.75 to 3.25	3/4 sq	0.75	0.4259
3.25 to 3.75	7/8 sq	0.875	0.4963
3.75 to 4.5	1 sq	1	0.5667

Key sizes are nominal square stock; widths and depths are in inches. Depth is the slot depth cut into the shaft.

End vs captivated keyseats

An end keyseat runs off the end of the shaft, cut with an end mill or a woodruff cutter so it is open at one end for the key to slide in. A captivated (closed) keyseat is a pocket with a rounded runout at both ends, milled into the middle of a diameter so the key cannot walk out. The configurator supports both; pick coverage when you place the feature.

A key length rule of thumb is about 1.5 times the shaft diameter, enough bearing area to carry the torque the shaft can. Longer than that adds little because the load concentrates at the ends of the key.

Frequently Asked Questions

A 1 inch shaft takes a 1/4 inch square key. The shaft keyseat is 1/4 inch wide, and the cut depth is on the schedule above. Enter a keyseat on a 1.000 diameter in the configurator and it uses exactly that width and depth.

By convention the keyseat is the slot in the shaft and the keyway is the matching slot in the hub or bore. They share a width (the key sits in both) but the depths differ. We cut the shaft keyseat; the hub keyway is machined to match on the mating part.

Yes. A captivated keyseat is a closed pocket with rounded ends milled into the middle of a diameter. Choose captivated coverage and set the length and offset, and the key is trapped between the two ends.

The schedule here is the square series, where width equals height, which covers the shaft sizes we turn. Rectangular keys exist for larger shafts than this schedule covers.

These references are for specifying a part; every value here is one the configurator applies when you build one. Numbers are representative of the standard and confirmed against your part before machining. See all guides on the guides page.