I didn't notice the 38mm ID in your original post, so Danno is right you can't thread it, nor will common threadless cartridge BBs work.

I second his suggestion, but you can't use an interference fit. The insert's wall is too thin and if you try to press it in it'll either buckle, or more likely shrink in making the thread undersized. Best bet is to turn it down to a precise non-interference fit and bond it, or if it's steel, spot weld or silver solder in.

If you want to bond it, you can have a straight knurl at the ends, but will have to do the knurling with a threaded cup installed to support it during the knurling. Properly done, with clean seufaces and the proper adhesive, bonding should hold up fine. After all there's plenty of surface area.