257 G/SH ST 2-1/2 C-KEYED

Permco's 257 series uses specific shaft and keying configurations, and the 2-1/2 C-keyed designation on this part matches that setup directly. If your existing pump carries that same shaft size and key type, this would be the corresponding replacement. Worth confirming your current shaft measurement and key slot match before ordering, just to be sure nothing's been modified on your unit over time.