Brake light switch -wrong part

[Mid Mod Guy]

The brake lights no longer work on my 63 Avanti. I checked the fuse, it looked fine but I replaced it with a new one. That did not solve the problem. So I ordered a brake light switch and went to install it and discovered that the threaded part is too small in diameter and does not fit or match the old part. I checked a couple different sources and they all give me the same part numbers and the same part as the one I already have in my hand. What’s going on? Is it possible? I have a non-standard master cylinder? I don’t think so. Here’s the new part that I have that does not fit.