Sign of the Crab Clawfoot tub Compression Stem.
These stems are found in various applications, including the P06, P12, P30, P558, P400, and others. If your handle spins more than 1/4 of a turn, this may be your stem. Sold by the each. Stem is 1 7/8″ long, 16 spline, 3/8″ stem Shank.
The other Sign of the Crab compression stems are #86-457721H and #86-457722C