Please note that the PICTURE UPLOAD function is not working. The iBoats Forum Moderators are working with the system administration folks at the parent company to get the issue resolved. This happened about a year ago and here we are again. In the meantime you can post photos as links to a picture hosting site of your choice. We are sorry about the inconvenience and will advise when the issue is resolved. Thank you for your patience.
I am thinking some were 1/16 -27 NPT. Thats pretty small as far as pipe taps go and not on a lot of charts. Had an 85 hp from the early 70's but I don't remember for sure. If you need any info on correct tap drills let me know. If memory serves me correctly you can even get by with a 1/4-28 straight tap in an emergency for a 1/16-27 NPT. Don't quote me on that I would have to look it up or try it on scrap to be sure. Let me know if you need any info and I can probably find it for you regarding taps etc. Best of Luck.
There are definitely 1/16-27 pipe taps. I have one and I am looking at it right now. 1/4-20 tap would be for a common 1/4 inch screw. 1/4-20 NC (or National Course) to be precise which is one of the most common screws in the USA. A 1/8-27 NPT (National Pipe Taper) as 14ftgruman correctly states is very standard. I have seen many 1/8-27 fittings with a 1/16-27 zerk tapped into it at a right angle to make a right angle fitting.
Check some charts. If they are 1/4-20 then they are NC not NPT which means they are straight. If it is a 1/4 NPT then it is a 1/4-18 NPT. You may very well have some grease fittings that are 1/4-20 but as I stated they will be a straight thread not an NPT or taper thread. iwombat states in the original post they appear to be NPT.
