Reximex RP, Mito, Paganax, Brenta, single shots insert 4,5 mm (177)

You need:
Copper wire or other wire, approximately 1.6 mm in diameter
1.5 mm drill bit
6 x 1 mm O-ring
Glue for attaching the anvil cover (optional)

Alternatively (depending on the filament and printer), gently lick with a file to align the "anvil" with the "body" and the bullet hole.
Connect the anvil to the body and chamfer the holes with a suitable drill bit, for example, 1.5 mm² copper wire