Keyway & parallel key sizes
A 25 mm shaft takes an 8 × 7 mm parallel key, with the keyseat cut 4.0 mm deep into the shaft and 3.3 mm into the hub, per DIN 6885-1 / ISO R773. Enter any shaft diameter and this page returns the standard key cross-section and the two keyseat depths — the lookup you would otherwise do at the machine.
Key width and height step up in bands by shaft diameter, so a nominal shaft size maps to exactly one key. The shaft and hub depths together clear the key height, so the key fits as specified by the standard.
How is keyway size chosen for a shaft?
Parallel-key standards tabulate key width × height against shaft-diameter ranges, not a single diameter — every shaft in a band uses the same key. A 25 mm shaft falls in the >22 to 30 mm band, which calls for an 8 × 7 mm key. The width is machined into the shaft with a keyseat cutter and matched in the hub bore.
Depths are given two ways: the shaft keyseat depth (how deep the slot is cut into the shaft) and the hub keyseat depth. Drawings sometimes dimension the shaft as d − t1 instead of the depth itself; check which convention a print uses before inspecting.