bolt size for hitch?

[gr8wi9]

I'm trying to install my Curt hitch and can't get the bolts in. I got one started about 2 threads worth, but that's about it. I sprayed WD40 to clean the crud out first. Anyway, I measure the bolt thread diameter at 11.7 mm, and count 8 threads per cm. So this would be a 12x.8 I guess. Anybody know if this is correct? I can go the hardware to try sizes, but if someone knows it would be easier.

thanks,
Jim

[robo5]

Hang tight. I can't remember the size off hand. 12X1.25 12X1.5 ? Was this the hardware that came with the hitch that you are trying to install?

What year is the van (new or used)?

IF the van has some miles on it, the threads on the body may have to be cleaned up with a "TAP". This will make a big difference on the install.

Someone will chime in with the correct thread pitch(if i don't get back sooner)


EDIT: Check out the first link it has instructions and hardware numbers http://siennachat.com/forum/index.php/topic,597.0.html

[scubajoe]

I could measure the bolts that came with my Curt hitch, but that probably wouldn't help. I re-used the bolts that were used with the old hitch. I guess we could compare to see if we got the same bolts.

[scubajoe]

Package of bolts says "M12 - 1.25x40 hex". Head of the bolt is marked JD 8.8.

[robo5]

Package of bolts says "M12 - 1.25x40 hex". Head of the bolt is marked JD 8.8.

correct!!! thanks

I would still run a tap into the threads. This will help in making sure you have a proper torque on the hitch.

[gr8wi9]

Thanks guys. I'll go to work cleaning the threads. BTW, I've made "single use" taps before by grinding a slot or two with a dremel tool in a bolt instead of buying an expensive tap.

Jim

[brian_bp]

...Anyway, I measure the bolt thread diameter at 11.7 mm, and count 8 threads per cm. So this would be a 12x.8 I guess. Anybody know if this is correct?

Metric threads are specified as millimetres per turn of the thread, the inverse of the inch system of threads per inch. Thus, 8 threads in 10 mm is 10/8 = 1.25 mm pitch (instead of 0.8 threads per mm)... and the bolts are M12x1.25 as confirmed above. That (and the 40 mm length) is also given in the installation instructions for the hitches.

[brian_bp]

Package of bolts says "M12 - 1.25x40 hex". Head of the bolt is marked JD 8.8.

The "8.8" marking is the class of the bolt material, by ISO standards. In rough terms, a lower first number would not be strong enough, and too high a second number would indicate a material which is potentially too brittle. Fortunately, 8.8 is probably the most commonly available grade of bolt.

By the way, I think it is supposed to be M12 x 1.25 x 40... a "x" rather than a "-".

[brian_bp]

Thanks guys. I'll go to work cleaning the threads. BTW, I've made "single use" taps before by grinding a slot or two with a dremel tool in a bolt instead of buying an expensive tap.

Jim

If the threads are just dirty or slightly corroded, rather than distorted or otherwise damaged, I would rather keep a cutting tap out of them. In other discussions of this challenge, various round brush options came up, including the wires ones used to clean the inside of 1/2" copper pipe (Home Depot example), and some for gun barrels (depending, I suppose, on whether you are a plumber or a hunter).

The MacGuyver tap idea is well proven, but if there are burrs where the bolt threads are slotted, they could do more damage than good, so it's not one I would try without caution... I would at least run it through a disposable matching nut to make sure it runs well before putting it in the Sienna's welded nuts.

[scubajoe]

Package of bolts says "M12 - 1.25x40 hex". Head of the bolt is marked JD 8.8.

The "8.8" marking is the class of the bolt material, by ISO standards. In rough terms, a lower first number would not be strong enough, and too high a second number would indicate a material which is potentially too brittle. Fortunately, 8.8 is probably the most commonly available grade of bolt.

By the way, I think it is supposed to be M12 x 1.25 x 40... a "x" rather than a "-".

No, it says "-", but I was just copying what was on the installation instructions.