I was going to replace the outside spare tire rack 'security' lug nut and noticed that it is threaded on the outside as well as inside for the stud. I am going to replace with a standard lug nut, since I don't like the 'security' lug nuts because you never seem to have a 'key' when you really need it. I bought this Blazer used and of course it doesn't have a security key or a onwer's manual. I think the answer is the outside threads hold on the small dish style center hub cap. So the question is do I need the outside and inside threaded lug nut and is it a 'GM dealer only' item?

 

The outside thread was for small black platic lug nut caps that came with the suv, probably broke off or got lost over the years.

 

^^^This.

Tire shop jockeys would then forget about these plastic caps and then put the impact to them to remove them and destroy them or forget to put them back on period ( I know from having worked in a tire shop).

I found them to be a PITA and replaced all mine with set of chrome acorn style lug nuts.

 

My 03 Blazer has the four small black hub caps that fit over the inside wheel rims that are mounted on the vehicle. NO hub cap or lug nut caps over the spare tire on the rear carrier.

 

That was a good question as I was wondering the same thing.

 

I went to an Auto Zone today and got a standard lug nut by Dorman p.n. 611-109.1. It is the stock threaded-on-the-outside version for 2.49 each. I'll use that to replace my rear tire rack security lug. I also saw that AZ carries the black plastic caps that screw into the small hub cap on the stock Blazer. These cover the actual lug nut. This is also a Dorman product and you get five in a bubble pack for only 5.99, so for 23.96, you could have your Blazer looking like the day it drove off the showroom floor. Ask for part no. 711-020. Oh ,yes, they also have the chrome acorn lug nuts if you prefer those. I didn't get the price. But with those you do away with the plastic caps which as someone above said gets broken or lost very quickly.
Nothing to do with this thread, but I also got an AZ Duralast 'Made by FelPro' EGR gasket p.n. 70789 for the 2003 4.3L V6. I like Fel Pro gaskets. I will try to remove and clean the EGR in this week.