so, here is a picture of my (bare) axle for the spring perch mount. is this correct for a '15 to have the machined concave area? my perches are flat mount. any replies and or suggestions always welcomed. and yes, it is definitely on the top surface
It looks like someone just got overzealous with the countersink during the machining process. There probably has to be some corner break in order to provide for the radius where the shoulder of the perch bolt meets the shaft.
Did you say on a 1915 front axle. I think somebody was using a Model A Perch Pin, if so you could probably use a tapered washer to fill the tapered hole. JMHO
I have two '26 axles and one '22 axle, and they all have tapered holes on the top side. Not sure about '15 models. Any date marks on the '15 axle? Good luck.