I have 10 pens that will be engraved on the lower barrel. If I'm only sending the lower barrel to the engraver, is it OK to put a piece of masking tape and a number so I can match up the pairs after the engraving is done?
You could always use magic markers on the inside of the tubes after you have finished them. I use this method quite a bit and it works well and doens't interfer with pressing or gluing the parts in..