Cross Reference for Drilling/Tapping??

[JasonRR]

I cross-threaded the holes in an aluminum bracket and want to drill & tap it to the next larger size. The current size is/was 8mm x 1.25, and I'm wondering if there is a matrix or cross reference sheet that would tell me which drill bit size to use to go up to the next size bolt.

Anyone know where I could find something like that?

Thanks.

- Jason

[dsrtuckteezy]

METRIC COARSE SIZES
----------------------------
TAP DRILL
SIZE SIZE
----------------------------
1mm x .25 .75mm
1.1 x .25 .85
1.2 x .25 .95
1.4 x .3 1.1
1.6 x .35 1.25
1.7 x .35 1.3
1.8 x .35 1.45
2 x .4 1.6
2.2 x .45 1.75
2.5 x .45 2.05
3 x .5 2.5
3.5 x .6 2.9
4 x .7 3.3
4.5 x .75 3.7
5 x .8 4.2
6 x 1 5
7 x 1 6
8 x 1.25 6.8
9 x 1.25 7.8
10 x 1.5 8.5
11 x 1.5 9.5
12 x 1.75 10.2
14 x 2 12
16 x 2 14
18 x 2.5 15.5
20 x 2.5 17.5
22 x 2.5 19.5
24 x 3 21
27 x 3 24
30 x 3.5 26.5
33 x 3.5 29.5
36 x 4 32
39 x 4 35

[JasonRR]

So I need to get a 7.8mm drill bit, right?

Any idea where I might find one of those??

This is for a brake caliper relocation bracket for the 320mm front rotor kit on my DRZ. The bolt first passes through the mount on the fork tube (the V-shaped piece that the caliper originally bolted to), and the ID of that is meant to accommodate the 8mm bolt. Now that I'll be using a 9mm bolt, I'll need to "clearance" that. There's plenty of material there to get away with doing so, but I'm wondering what size drill bit to use. Something just very slightly larger than 9mm, I'd suppose, but I'm wondering if there is a similar guide?

Thanks!!!

[dsrtuckteezy]

5/16 is about equivalent to that...use that if you want and the appropriate bolt to go with...

[JasonRR]

I think I'm going to run to Fastenal tomorrow and see if they've got the actual bit. I really don't wanna fuck this up.

[turbostang]

Are you wanting to stay with Metric?

The simple math is this - .039375 X MM = standard size

So, in your case, right now - your OD is .315 (close to 5/16, which is .3125)

If you want to know the opposite, you simply switch your math around -
.3125 / .039375 = 7.936xxx (just under 8MM)

If you don't mind switching to standard, you can use a 3/8-16 bolt, which uses a .3125 tap drill size.

It's pretty easy, there's a million ways to solve your problem, you just have to pick one.

[JasonRR]

Thanks very much for the explanation, very helpful!

[turbostang]

Thanks very much for the explanation, very helpful!

No problem boss, good luck with the resolution.

[Nash B.]

zomg y r u teaching me algebra? i'll never use it in real life!

[turbostang]

zomg y r u teaching me algebra? i'll never use it in real life!

That's elementary math, no more than a metric/standard conversion. Something we all learned in 2nd grade or so.

[Nash B.]

That's elementary math, no more than a metric/standard conversion. Something we all learned in 2nd grade or so.

Well, you introduced variables, so it's algebra.

I (inches) = .039375m (millimeters)

[JasonRR]

I decided to not try and repair it after all, but am just going to pony-up for a new bracket ($100) instead. All of the other options just had too many compromises and/or risks, and since I'm pretty heavy and hard on my front brakes, I wanted to make sure and do this right.

Appreciate the help again though guys.

[turbostang]

no problem man, that's probably not a bad idea anyways.

[Grape]

my phone does that