I see older Wilton vises fairly often where it looks like the end cap pins kept working themselves out. On some the owner welded them to the static jaw support. I have a simpler and more effective way to take care of the problem so that the vise can still be taken apart and reassembled easily.
Eventually, the two 1/4″ pins that hold the end cap support and nut will either need to be replaced or taken apart to clean the nut. Wilton uses a straight soft pin that is drilled and reamed through the static jaw support, the end cap support, and finally the cast nut. This pin aligns two separate parts on the tail end of the vise. Two pins are used and must be removed by driving the pins out from one side. I have had a few that were tight and I had to remove them by welding a slide hammer to the pin and pulling them out like the welded ones.
This 5 inch vise takes a 1/4″ pin diameter drilled and reamed in line connecting the end cap housing and nut. I decided to assemble it a little more simply to make it easy to take apart.
I added a gauge pin so I could sweep in the pin with a indicator to pick up center Then I ran a tap through the static support. Take a thickness dimension of the static wall thickness so you know how deep to tap . You can also do this with a heavy duty drill press. It just takes longer to set up.
I like to hold the nut in by jamming a piece of wood in the end. The two pin sizes I have seen are 1/4″ for the larger vises and 3/16″ for the smaller vises. These two size pins are perfect for a 5/16:18 (tap drill .257) and a 1/4:20 (tap drill .201) thread size.
I purchased some long set screws from McMaster Carr and chucked them up in a lathe and turned the ends down to 1/4 (.250) of an inch to slip into the reamed portion of the assembly, tap drill size for a 5/16:18 thread is .257. Another way to turn the 5/16 set screw down to a 1/4 inch is clamp the set screw in your drill press and use a disc grinder and slowly grind down the threads to a 1/4″. Take your time and check often with a set of calipers or a micrometer. That is how I made the ones in the picture.
Pretty simple fix and real easy to disassemble.