Preupdate XJ oem lug nut size
 

Something that I haven't done for a while, is check the tightness of the lug nuts on my oem 15" Jeep Steelies. The reason for checking is that I could hear noise from one of the rear wheels. I found a loose nut and tightened it. Then I decided to check the others.

I got to the last lug nut on the front pax side using my Jeep supplied onboard 19mm wheel tool and to my surprise, it would not fit over the nut.

I then checked it with my wheel brace (which lives in my garage) and a 21mm socket was needed for that last lug nut. Great, I thought. That would have been an unnecessary call-out for road service if that tyre ever got damaged. If I was in the middle of bugger all, that could have been a problem (without the brace).

Over the years, many of the original lug nuts have worn, and been replaced by basic 19mm open ended nuts.

I am thinking of getting some new replacement oem style lug nuts to put on all 4 wheels. It's the detail that matters.

What is the size of the default oem lug nuts on pre update models with the sport 15" Steelies?

Is it 1/2 - 20 (3/4 Hex) for the 19mm?

I think the 21mm converts to 13/16 Hex.

That's all correct. 7/8 is just over 22mm so 13/16 should be just below 21mm.

I dropped into several auto parts and accessories stores today in search of the elusive 19mm lug nut.

As rare as hens teeth. No wonder the 21mm nut has made an appearance on one of my wheels.

Looks like an eBay or rockauto order.

What is heat treated chrome? Is it better than chrome? What about zinc? I used to think lug nuts were just lug nuts and chrome was chrome.

I would expect heat treated to be harder and more corrosion resistant.
Zinc coated nuts might corrode quicker than chrome, but then again might not. Depends on the chrome/zinc quality.

If you want the best quality lug nuts available I'd have to suggest McGard.
I have a pic somewhere of an old chrome lug nut vs a McGard nut and the cheaper nut is rusty and has the chrome flaked off it.

When I bought my current McGard nuts I bought a pack of 100 from rockauto and batched the extras up. Gave one set to a guy who used his Jeep for charity work, sold the others on ebay to make mine essentially free.