Craftsman 12" radial arm saw

I have this 12" model number 113.29500 Craftsman radial arm saw. On the und erside of the arm is a hole. About 1/2" wide by 4-5" long. Everything tells me it was from the factory that way. The arm is grey in color even in the opening. Can anyone tell me why they would put that there for. I can even s end you pictures of it.
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