I thank you in advance for the answer.
I have the above mentioned 1pc 15x10 3000lb rated MT -ALCOA wheels.
MT can only tell me it uses a 60* conical nut. That I know. I called Alcoa but that was a dead end as well, had a good feeling thT was going nowhere.
Can someone tell me the PURPOSE of washer 'recess' is on the backside of the rims? Is this a sacrificial piece to prevent galvanic corrosion BT the wheel and my rotors/drums? I'm putting them on a 76 bronco with Duff long arms. Is the washer a structural aspect of the wheel when on the stud? I'm assuming this recess is for a washer of some sort. Please provide any info . Oilite washer? Steel or aluminum would kinda cancel out the galvanic corrosion aspect I brought up....
SIZE & type washer PLEASE?
Purpose bc I like to know WHY?
Thanks for your help!

 

A pic is worth a thousand words.

The only Washer i know of use on aluminum wheels is when the "MAG" style lug nut is used

 

If I'm understanding you correctly you're asking about the shallow counterbore around the lug holes on the back side of aluminum wheels. I can't say for certain what it's for, but I've never seen any washers or anything that needed clearance, so I'm sure it's not for that.

I suspect that it's just so the wheel contacts the hub farther away from the lug. But that's just a guess.

But there would be no problem putting those wheels on a '76 Bronco. There would be no washer of any type used. Just the wheel and the lugnuts over the studs.

 

NothingSpecial, YES I am asking about the 'counterbore'. Here are some pics I took last night. Along with some info on the wheel fwiw.
* Alcoa Forged - Max Load 3000lbs -Max PSI COLD 95lbs
U.S.A. - 0699 - PART NO. 250400 - 15 X 10 J *



I have this style wheel in 7-1/2" & 8-1/2" as well. The 7-1/2s do have a 1/2x20 nut that does "sleeve" the stud to center the wheel. They are not the Anson 'slots' but made by Rocket Industries IIRC.

 

Need to figure out how to add pics. I've got them in my cp and labeled, but says I need to up,lad them first before posting. I believe they are uploaded.

 

Is it possible those recesses are for washers that hold the rotor or drums on. It's like a twist lock washer.

 

Whatever they are for, you don't need to worry about them. Just put the wheel on.

 

No washer needed with those wheels. Just 60* acorn style lug nuts

 

It looks like your studs are too short in that one picture.

 

Sweet looking wheels!