Stupid metric bolt question

supraman1990

New Member
Joined
Jul 20, 2007
Location
Claremont, NC
I'm trying to put the rear bumper back on my CJ that I received when I bought the Jeep, and am having a hard time finding bolts that work right. I can spin a 1/2 by 13 bolt down until figer tight, but the instant I put the ratchet on it the bolt slips as if something is stripped. It does this on every single one, so I know it isn't just 1 bad bolt. Any ideas? I was thinking that it is possibly metric, but I have no idea what size metric it would be, and I'd rather not carry my 50+ pound bumper in to the store to get the right part.
 
When you say 1/2 by 13, do you mean it has a 13 mm head and it's 1/2" long? 13 mm is functionally identical to 1/2" - are you holding a metric bolt, or SAE bolt? D you you know the theead pitch on it?
What bumper are we talking about here, something original that should be SAE, or recent/homemade aftermarket that's probably metric?
 
When you say 1/2 by 13, do you mean it has a 13 mm head and it's 1/2" long? 13 mm is functionally identical to 1/2" - are you holding a metric bolt, or SAE bolt? D you you know the theead pitch on it?
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He has a 1/2" bolt, so it is SAE, the thread pitch is 13.

There is not really anything close to 1/2" in metric. 12 is smaller and 14 is bigger.
 
AlphaFourWheelDrive said:
He has a 1/2" bolt, so it is SAE, the thread pitch is 13.
There is not really anything close to 1/2" in metric. 12 is smaller and 14 is bigger.
Click to expand...

And 13mm is almost exactly the same as 1/2". 12.7mm = 1/2".

I'm just trying to get a little clarity here.
Are we talking about a 1/2" bolt (shank fits 1/2" hole" or a 1/2" head (so the shank is prob 3/8")?
The thing is, most metric threads for automotive use is 1.25, except really big and really small bolt. If I understand the situation correctly, the thread pitch is the same (or very close) but the diameter is just a little different.

IIRC, you have a similar situation to this with an M12 (14mm head) bolt and a 7/16 (5/8 head) SAE? I know this due to the only SAE bolts on 4Runners (rear seat belts and on the rollbar).

I'm kind of wondering if the threading is for an M14, that'd be only 1mm larger than the 1/2" bolt you have. Metric "course thread" is 1.5 IIRC? Wonder if that closely matches SAE 13.
 
so your trying to find nuts instead of bolts then?
cause either way if its a stud a nut thats 14mm will likely be too big and if its a bolt it will probably be like wise.
 
A CJ would have metric fasteners??
 
WHAT IS THE FASTENER SET UP!

does the bumper have studs welded to it that you run a nut down on it? What's the deal?

can you take the hardware and run it down while it's off the jeep to see if you do in fact have the right size nuts bolts/studs

confirm (OFF THE JEEP) that the nuts and bolts/studs to match.

again, EXPLAIN HOW THIS MOUNTS! studs, bolts, nuts, factory brackets, aftermarket brackets. Factory CJ just use nuts and bolts thru "L" Brackets, does yours work the same? It may not be the bolts and nuts at all, but the rather the nut behind the ratchet doing something we can't see thru our monitors.
 
mbalbritton said:
WHAT IS THE FASTENER SET UP!

does the bumper have studs welded to it that you run a nut down on it? What's the deal?

can you take the hardware and run it down while it's off the jeep to see if you do in fact have the right size nuts bolts/studs

confirm (OFF THE JEEP) that the nuts and bolts/studs to match.

again, EXPLAIN HOW THIS MOUNTS! studs, bolts, nuts, factory brackets, aftermarket brackets. Factory CJ just use nuts and bolts thru "L" Brackets, does yours work the same? It may not be the bolts and nuts at all, but the rather the nut behind the ratchet doing something we can't see thru our monitors.
Click to expand...
Pictures are good. Heres an MS paint version of the bumper
bumper.jpg

The black dots are studs in the bumper, non-removable, they are welded in. It's some sort of after market bumper. The studs are just that, studs. I am looking for nuts to go on to the stud to hold it on. Other questions?
 
So what you really mean is that a 1/2" 13 NUT is just a little too big to fit these studs?
Am I correct in udnerstanding that these nuts you are using will spin down ok (so the thread pitch must be close), but pop when pulled tight?

If that's the case, then try M12. Thread pitch would be 1.75... seems kind of far from that 13 but maybe close enough to work.
If aftermarket, an M12 is not undreasonable, ANSI spec would be an 18mm head (j-spec is 17mm).
 
RatLabGuy said:
So what you really mean is that a 1/2" 13 NUT is just a little too big to fit these studs?
Am I correct in udnerstanding that these nuts you are using will spin down ok (so the thread pitch must be close), but pop when pulled tight?
Click to expand...
Completely. They get down to hand tight, but when I put the ratchet on it pops. Suggestions? 12MM, 14MM?
 
I don't know where Claremont is, but drag that thing to my house. I got a big enough assortment we can get that thing bolted on.

seriously, PM me if you are interested in that offer.
 
mbalbritton said:
I don't know where Claremont is, but drag that thing to my house. I got a big enough assortment we can get that thing bolted on.

seriously, PM me if you are interested in that offer.
Click to expand...

And if he dosn't have something to fit, fire up the welder and avoid the issue altogether :beer:
 
you could always tap it to a standard size.
 
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