tail light socket question

When i was redoing the tail lights on my '72 Bbody I found the sockets I purchased to replace the factory ones were just a tiny bit different and would not fit (too loose). The back-up lights did fit, the others did not. Did my best to clean the rust out of the old sockets. Almost destroyed my factory sockets trying to remove them at first. Proceed carefully because you might find that what appears to fit/work really does not.