Hey I just got 19x9et34 19x10et40 Apex EC7 wheels and they say you need a stud conversion for the front and rear because the stock ones are too short, first off I went and bought the is300 set of 4x studs and only 10 of the studs fit in the front, the back studs are different and for whatever reason there is nothing on the forums saying people needed something else. Then I bought another set online that looked like it would fit but I was wrong so now I'm down about 800 in labor and extra studs, if anyone knows what I could do let me know. Attached image is the stock rear studs 12.1mm around the neck or so.

 

I required wheels spacers for the rear of the F. I bought a kit where it all came together.

PN 30656014
$159.00
H&R DRS TRAK+ WHEEL SPACER

If you are aiming to use the stock wheel nuts (I do when I switch back to stock wheels over the winter), the thread size and pitch must be 12 x 1.5 on the new studs. Just remember that the stock wheel nuts cannot be used on aftermarket wheels. If you are planning on scrapping the original nuts, then you can technically go for any 12mm stud you like, but I do not recommend this. To sell the car you may want to be able to fit stock wheels again.

 

Do you have aftermarket replacement wheel hubs/bearings installed? The factory studs should all be the same. You could possibly drill out the hubs to fit proper studs. The only time I've ran into issues with studs on previous cars was when the wheel bearings had been replaced. The stud in your picture does not look like the factory part.

I've swapped out the studs on mine for the longer ones that came with my H&R wheel spacers. The studs work fine for my Apex wheels as well.

Here's a comparison of stock, H&R, and ARP stud lengths.



I think the factory ones are so short because of the style of lug nuts used on the factory wheels. The tapered cone nuts of the Apec wheels would only have a few threads of engagement, so you really do need longer studs. The factory nuts protrude into the wheel and have far more lug stud engagement.

 

On a hunch I checked out wheel bearing replacement options on Rock Auto. Almost all of the standard/higher quality options match the OEM style & size of the lug studs. Notice the "nose" at the end of the threads in my image above. Plus they all look to be ~14mm shoulders.

However when you look at the economy bearings, several of those seem to match the stud shown in the OP. Ie: No nose on end of threads and appear to have much narrower should diameters.

I almost never look at economy options so didn't notice it at first. Yet there's a pretty noticeable difference between a Timken hub that costs $188 vs an economy option that costs around $40.

To me, it appears that one or both rear wheel bearings were replaced at some point with economy rated parts.

You have two options to fix this issue: a) drill out the current hubs to accept the ~14mm shoulder of the lug studs, or b) replace the whole wheel bearings with OE rated parts (Timken being my suggestion) - swapping studs will actually be a little easier with this option since it can be done on a bench before installation.

Extra note on the Apex wheels. Mine are dedicated for track use, so I do swap between those and the factory wheels for track days. On the rear, I can only run a 10mm spacer with the H&R studs. Normally on my stock wheels I run a 15mm spacer. I got the ARP studs to possibly go up to a 15mm spacer with the Apex wheels, I just haven't installed those yet. Some quick measurements had me a little concerned I'd need to cut them down a few mm to run the factory wheels/lug nuts and I just didn't want to deal with it last weekend. I did take actual measurements of all three studs, will update this comment when I get a chance to look at my notes in my tool box. Figure it'll be useful because for some reason ARP specs are listed in inches, and I couldn't find any info on the longer studs that H&R includes with their wheel spacers (for the much safer DRS slip-on style).

 

How exactly are the rears not fitting? The knurled part too big in diameter? Or the stud is too long to get it inserted from behind. I know with ARP studs, the rears need to be trimmed a little or the hubs need to be removed. I have ARP (IS300) studs on both my RC F and IS F.

Edit: like @LoSt180 said, you may have aftermarket rear hubs, the knurl diameter of the arp stud
or OEM stud is too big for your rear hub flange. So like he said, you can drill the holes to proper diameter or find studs with the correct knurl diameter. Looked through summit racing list of arp studs with 12x1.5 thread and found some with knurl diameter of 12.3. OEM is 14.xxmm IIRC.