Shel, please note, this is our U4 pump assembly. It is intended to only be used as a replacement pump for our C202H or the old C201H. The pump head casting has multiple bosses for drilling and tapping. We only drill and tap one boss that is for our C201H/C202H compressor. It sounds as though you may be trying to use this in a different application. If you need additional replacement part assistance, feel free to contact our product service team at 1-888-895-4549 or service.parts@sanborn-mfg.com. Thank you for your time!