Well, my curiosity got the better of me, and here's what a quick search of tholepin (not to be confused with solepin) turned up:

peg, pin, thole, tholepin, rowlock, oarlock -- (a holder attached to the gunwale of a boat that holds the oar in place and acts as a fulcrum for rowing) PART OF: dinghy, dory, rowboat -- (a small boat of shallow draft with cross thwarts for seats and rowlocks for oars with which it is propelled)

http://www.notredame.ac.jp/cgi-bin/wn?cmd=wn&word=tholepin

I'm fairly certain that either thole or tholepin is also the word for the pin on a scythe. Not certain at all about what relation, if any, the tholepin may have to the heel of the scythe.

WW