Drill diameter needed for 5-40 in sst.

[gstours]

I've got to tap a hole in a pc of 302/304? Stainless steel approximately 3/16 " thickness.  What drill size would you recommend?  I have always had a hard time with this.  Just wondering?🤔
   Any tips would be helpful.  🙈.    Thanks.

[STRIPER LOU]

Hey Gary, for general use a #38 (.101) is recommended but for SS I use the next size #37 (.104). I just did a bunch of holes a little while ago.

This works well for me. Sharp tap and plenty of lube.

..................Lou

[Three se7ens]

0.104" #37 is what Id recommend as well.  That gives you 65% thread engagement, which is plenty in harder materials. 

Be sure to use a good, sharp drill and cutting oil.  If you work harden it when drilling, you will have a harder time tapping it. 

[Tiddlerbasher]

Try and use a hss co tap - ie a cobalt one -they are worth the extra $

[Tiddlerbasher]

Also for stainless I am using pretty much only cobalt hss drills as well - thay last a lot longer - well worth the investment

[gstours]

Thanks,  the advice is well received.  You folks are great 👍🌊🌊🌊.   I will get a going.  Find the number drill box.🍀