Acceptable tolerances for matching taps and drill bits

[FGarbrecht]

I'm trying to get my head around how close the tolerances should be when selecting drill bits for specific taps. To be specific, I want to make a FP section to accept a Bock feed housing, so I have to use the Bock specific tap for the interior section threads, which is M6.4 x .6. The optimal bit should be 5.8 mm (6.4 minus 0.6), which is 0.2283 inches. Should I just buy a 5.8 mm bit or is it acceptable to build in a little slop, and if so, how much slop is OK and still get a nice fit? For example, an "A" bit is +0.0057 oversize, a 7/32" bit is -0.0096" undersize, and a 15/64" bit would make a +0.0061 oversized hole. I'm not a machinist so I don't have a feel for these tolerances, but I also don't want to buy every drill bit known to man and drill a zillion experimental blanks to find out. Any thoughts appreciated!

 

[Curly]

When it comes to metric taps if you need to buy a bit to use it get the metric ones. So get a 5.8 and a 5.9 for one size bigger hole. The 0.1mm is close to .004" so each step is predictable. If you already have sets of letter, number and fractional bit play with them. Those bits from Victor are under a couple bucks each so you'll need to get a few items to reach their minimum. If you have a machining tool supplier near you you can just go get them for a little more each. https://www.victornet.com/subdepartments/HS-Jobber-Drills-Metric/1170.html

 

[Dalecamino]

Visit this link. You can print it out. Tap, drill chart.

Tap & Clearance Drill Sizes

This tap and clearance drill chart shows tap and clearance drill sizes for standard threads. There is also a printable version that has both metric and inch threads.

littlemachineshop.com

 

[eharri446]

According to the people at Beaufort Ink, the Bock #6 requires a 5.9mm drill bit. It seems that there is a small bump that will not fit into a 5.8MM hole.

 

[BEW-NZ]

Thank for publishing Drill sizes and the recommended clearance size.