Greedy

I started up my freshly rebuilt 5vz tonight and it started on the first try and purrs nicely. However, there is a small oil leak coming out of the oil pressure switch. I put it on with a large cresent wrench while I had the motor out of the truck, but now can't get it in there to tighten it down. I am going to go get a deep socket to tighten it down but can't tell what size it is. Does anybody know? Thanks...