I am restoring an old combo tool which has a non-standard 5/8 18tpi threaded shaft, I need to find a 5/8-18tpi threaded mount drill chuck but can't find one. I am hoping that someone will be able to help. If I could find a 5/8-18 to 1/2-20 coupling adapter I could make a work around but I can't find that either. I appreciate any ideas. Thanks for your help, Mike