Todd:

I believe that your photo is the stock wiper arm replacement. If you have the stock (original) wiper drive it has a ¼” diameter post that sticks through the cab above the windshield. This post has a 1/8” hole running crossways through it. The hooked end of the wiper arm passes through that hole and the spring is slightly compressed holding the arm in place.

BUT if you have a modified wiper drive you will see a ½” diameter serrated drum sticking out above the windshield. This is an adapter to allow the use of the much better later design arms.

The drum is slipped over the original ¼” post with a 1/8” pin holding it in place. If this is what you have you can use the newer stile arms

1941 Chevy Master 3/4-Ton
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Born to fish, the truck is only a hobby.