Metric Bolt Size

I am working with a bolt that I thought was 3/8" course thread. Well come to find out it is a Metric size. Anyone know the Metric equivalent to a 3/8" X 16 bolt???
Thanks,
Rich

10mm is .022" larger than 3/8" 16 pitch is close to 1.5 mm pitch. 1/16th inch is .0625, 1.5 mm is .059" Close enough to look right but not close enough to fit.

Gerald J.

You need to get out the calculater &make a chartfor future referance.
This is what I did many years ago when I first started to encounter metric fastners.
A starting place is to remember that 1mm=.o3937 in.
I still use my chart as I never can remember all the different sizes. CRST set in a long time ago. HTH

years ago I swapped out a 3.8 V6 in an F-100 for a 302. I re-used the bellhousing and bolts. They seemed to tighten up fine and I didn't know the v-6 had metric bolts. they wound up working loose and breaking the aluminum bellhousing.

M10 X 1.5

Big question is what are you working on?? Could well help because lot of us work on so many things that we may know right off the top of our heads to what you need. Of course we may not but hey if you tell the whole story it could well help

It might also be 10 X 1.25.

For standard bolts, (cap screws) if the heads are marked with lines they are inch sizes. If they have numbers on them they are metric.

THREAD DATA CHARTS - does it help ?

i can tell the diff. by the heads.the bolt dosnt even look like the standard thread ones.

The numbers on the heads refer to the grade or "hardness" of the metric bolt.

I went through this exercise a couple of months ago. Replaced a brake caliper on my Ram. It bolted right up to the chassis just fine. Apparently there are two variations of caliper for this truck. The problem was with the banjo bolt holding the line fitting to the caliper.

The reman caliper was tapped for 3/8"-24 (NF). The original was metric 10-1.0 Close but no cigar. That 1.0 thread on the banjo bolt was CLOSE to a 24 pitch, and the 10mm just enough larger than 3/8", that it would seem to start in okay, but start to bugger up and jam after just about 3/4 turn. A quick check with a 3/8"NF bolt I had laying around was just enough smaller in the fitting to convince me that the difference was more than I wanted in a critical system like my truck brakes. I went back and got the correct caliper. The banjo bolt was probably okay, long enough that chasing off the slight damage to the threads at the end likely wouldn't have hurt a thing, but I replaced it, too.

In short, there may be one or two bolt sizes in the universe of such things that would give you a direct fit between metric and English, but yours isn't one of them.

You don't say what you're working on, but if it's not a specialty item, metric bolts are easy enough to come by. Any hardware store with the aisle full of the racks with the little drawers of nuts, bolts, washers, shelf brackets, springs, clevis pins . . . should have a decent assortment.

Quoting Scotty:
"In short, there may be one or two bolt sizes in the universe of such things that would give you a direct fit between metric and English, but yours isn't one of them."

I fully support your observation. We are a "metric" country and have run into the same problem as throop many times, albeit from the other side. We had and still have tractors and implements from the USA, Canada, and the UK and I NEVER found a threaded part that would work in the other threading system.
Even for regular wrench sizes there is very little commonality. A 3/4 inch wrench fits a 19 mm nut very well and vice versa. It is off by just two thousands of an inch (or 0.05 mm).
Hendrik, from The Netherlands.

Oh, I hear ya!

As a result of the US's supposed commitment to go metric, back in the 70s I believe it was, we've got an awful mishmash going here. Motor oil is still sold in quarts. Soft drinks and liquor (no more half-gallons, quarts or the handy, fit-in-your-hip-pocket fifths) are in metric.

On vehicles and machinery, there's plenty of both on any given vehicle. A fellow wants to have a full set of both wrenches on hand for a single project (like my brakes).

I did learn, in trying to noodle out the issue with that banjo bolt, that my 19/32", 1/2" drive socket from the Craftsman set that I bought back in the late 60s, makes a fine match to the 15mm head on a 10mm bolt!

I did inquire over on Tool Talk a while back about just how that set happened to include a 19/32" when it otherwise went by 1/16ths. Learned that Ford used that size for their rod cap bolts. Similarly, in my old deep-well sockets, there was a 25/32" that was for a particular nut in the suspension. Both sizes are rarely seen and hard to come by any more. I guess a fellow could substitute his 15mm socket for the 19/32" in a pinch, eh?

Scotty. While I agree on a person being able to substitute a 19/32" socket for a 15 mm, you have me puzzled about the wrench size for a 10 mm bolt. All standard M10 bolts and nuts take a 17 mm wrench, not 15. I know of only one use of my 15 mm wrench: axle nuts on a bicycle with 10 mm fine metric thread. These are not (ISO)standardised, only a sub-standard in bicycle world, possibly also a standard in brake caliper banjo world... My 2 cents.
Cheers, Hendrik