Hi guys, I have a Smith & Wesson 3rd model double action top break 38 that I'm toying with. I've found myself a new barrel but I need to get a base pin for it, kinda hard to come by. I have an extra barrel to donate one but am not quite sure how they are held in. Are they threaded? Pressed in? I've looked at different drawings and seems that there were both but my new barrel has no threads in that hole. I have tools and skills, just don't wanna have a mishap. Any help from someone who's done it would be greatly appreciated.

Thank you and have a great Memorial Weekend.