As the cast-in text says, this is a compound ladder lock. I fiddled with it for a few minutes and couldn't figure out how it might work, maybe it ties together the two parts of an extension ladder or maybe two ladders?
According to the company history Elijah Spare came to Cambridge Massachusetts from Vermont in 1839 to build a church. Story is he couldn't find a ladder so after the church was done he stayed in Cambridge and started the first American ladder company. The company is still in business today.
All I can contribute is a patent drawing showing how they probably worked in general, but this may not be the same version of the lock you were looking at:
ReplyDeletehttps://patentimages.storage.googleapis.com/39/fa/b1/5e3a3122bf415d/US556831.pdf