3/8" Conical toothed washers

I ordered a trailer hitch installation kit from U-Haul to do the installation myself, but it came with no hardware. The hex bolts are pretty standard, but it also calls for “3/8” conical toothed washers," which they don’t carry at Home Depot. Anyone know where I could pick some up or order online?

Some ideas
McMaster-Carr - http://www.mcmaster.com

Grainger - http://www.grainger.com

Local auto supply store

And, wait for it, go to any place that installs hitches

try etrailer.com

Ace Hardware ?

Ace didn’t have it.

No to auto parts and hitch installers

– Last Updated: Jun-04-13 2:25 PM EST –

I had already tried them before posting this thread. O'Reilly's Auto Parts didn't have them, and I called the U-Haul that does hitch installation nearest my house and they said they can't provide me with hardware unless they were doing the installation themselves, because UHaul doesn't send them extra parts.

Thanks for the links, but unfortunately looks like McMaster doesn't have them at all and Grainger only has nonserrated.

Hmm, looks like they don’t have 3/8
This is frustrating.

Do without until you can find them?

– Last Updated: Jun-04-13 6:36 PM EST –

I just looked at an online video showing hitch installation and the use of those washers, and I really wonder how necessary they are. Maybe the purpose is to make sure the clamping force does not occur primarily at the edges of the bolt hole, but is a similar device provided on the other side when mounting to unibody cars, where THAT sheet metal is many times thinner than that of the hitch frame? The thinner the metal being clamped, the more need there'd be for this sort of thing.

I've probably seen hundreds of hitches mounted without conical washers, many being very heavy-duty units. I've seen some hitches (and home-built bumpers too) that undergo enormous shock loads and standard bolted connections have been just fine. I'm sure you could do fine with standard washers as long as you make sure the bolts are plenty tight (lubing the threads will go a long way toward insuring you get enough tension in the bolt, because that way thread friction won't be great enough to fool you or your torque wrench into thinking the connection is tighter than it really is). If you get the chance to replace the standard washers with conical ones later, and I'm sure you can if you keep searching, it'll be very easy to do (one bolt at a time so you don't need to actually reinstall the hitch), and in the meantime you'll have a fully functional hitch that's just like so many of the ones already out there that are working fine.

bolt & nut torque specs. …

– Last Updated: Jun-05-13 12:29 AM EST –

....... dry torque spec is not the same as wet torque spec .

Most common torque specs are dry torque (unless spec. specifically noted "wet torque") , so if you lube the bolt and apply dry torque spec , you "will" over stress the bolt and threads . Over stressed bolts can and do fail . Sometimes it shears as you are installing it , sometimes the threads wipe out , most times it fails under a service load .

Wet torque is always notably less than dry torque .

The idea of torque"ing" a bolt/nut , is to put it under enough tension to "stretch" it just the proper amount .

Most common hardware store bolts and nuts are junk for things like hitches and high service load items .

Use at least SAE grade 5 bolt and nut for your hitch connections , I'd opt. for SAE 7 "better yet" .

"Don't use" common hardware store junk no grade bolts and nuts (they may claim an SAE 2 cause they are un-marked) but they are junk "toys" soft steel .

Any auto parts store should be able to provide you with SAE 5 or 7 bolts/nuts .

And if your U-Haul hitch is calling for 3/8" bolt/nut , I'd definately go for the SAE 7 and the Toothed Conical washer .

Here's a chart to give you the idea ...


ps., ... the toothed conical washers are used to distribute the load , not just thicken the connection surface as flat washers do .

Good Info

– Last Updated: Jun-05-13 8:50 AM EST –

I surmised that the purpose was to spread the load, but I only suggested that it's okay to do without them until he can find them because so many hitches and hitch-like structures are fastened to vehicles without them, and who's ever heard of such connections failing in some way? It looks like a good idea to use them - I just wouldn't put up with not having the hitch that I needed in the meantime.

I mentioned lubing the threads because there are plenty of cases where dry connections really do make it difficult to get the "right" bolt tension on account of too much friction. Frankly, on new bolts, I don't think this will be a problem but it's probably worth being aware of. On steel car wheels that have gotten a bit rusty for example, the nuts can end up too loose due to "grabby" contact surfaces, OR they can end up being much too tight. They can end up too tight when while attempting to get a little extra turn on the nut, it suddenly "lets go" and squeaks as it slips. The extreme vibration that occurs while it squeaks will usually cause the nut to turn very easily for just an instant, and you can easily get an additional quarter turn or more than what you "should" before you even have time to back off on the torque. A bit of lubricant will mean the actual torque you shoot for is less, but at least you can achieve what you are aiming for without accidentally spinning it too far. I'm not saying this is "proper", but too-sticky sliding surfaces are a fact of life in real-world applications, and accommodating them in the most expedient way is better than sticking to rules that don't apply for THAT situation. It's a bit off the topic of NEW bolted connections, but since I mentioned it, that's how it can matter.

Ok, now I feel dumb
I had moved the hitch around several times in my garage since I had gotten it, no sound of anything rattling or moving around. Yesterday afternoon I picked it up and was really taking a hard look at it out in the sun, and happened to look down the throat of the receiver with the sun shining down there, and saw what looked like the corner of a plastic bag all the way down in the thing. Using a hemostat I use to get hooks out of fish, I pulled and eventually got the bag with all the hardware and instructions out of the thing. Problem solved. Man, they really shoved that down there.