How to mount cb antenna feed through adapter SO-239. High swr ?

A lot of people seem to be mounting this feed through adapter the wrong way, which directly shorts the antenna to the ground. Put the plastic washer on top of the mounting bracket. There's other things you can check for high swr problems as well. A cheaper multi-tester with "continuity" function can help out a lot to find out shorted coax cables, mounts, verifying your antenna is grounded, etc. Type of antenna, length of whip, position of antenna, badly soldered/shorted PL-259 connectors, length of coax cable...lots of things can make a difference, but usually can be worked out.