Tabulated depth control values for shaft keyseats and hub keyways are given in ANSI B17.1-1967 standard and this page has been prepared accordingly.
The distance from the bottom of the shaft keyseat to the opposite side of the
shaft is specified by dimension S. The distance from the bottom of the hub
keyway to the opposite side of the hub bore is specified by dimension T. For taper keyseats, T is measured at the deeper end. See the following figure for the dimensions.
Keyseat: An axially located rectangular groove in a shaft or hub. Hub keyseat has been sometimes referred to as a keyway
Sunk Key: A standard form of key with rectangular or square cross-section in which the key fits into the keyseats on the shaft and the hub.