Any one know correct size of lower control arm pivot shaft diameter on the taper which mates into the K member? I bought new control arms and the pins in them don't mate snug on the taper portion in the K member. They fit in and tighten only against the shoulder.

The diameter is tapered and measuring at its widest by shoulder:
My original pins are .945".
New pins are .925". Are all aftermarket pins this size?

The new arms will fit in K member as they are .020" smaller. But they don't mate into the taper and are loose. Instructions say to tighten to 145 ft lbs, and that is probably why its OK?

I will call MFG of the arms to find out why, but I would also like to see experienced opinion about this. Im worried this would wallow out the K member hole or be noisy.

You seem to know the answer to your own question. yes I would think .020 is quite a bit smaller and if it comes loose it will cause problems. why are you using aftermarket arms? why don't you use your old piviot pins? it might be some extra work but might be worth the effort. that's my option only.

What size is the hole in the K member? You may find that the OE pins were loose in the K member till you tighten the nut down as well.

I would share your concerns. A loose tapered fit serves no real purpose. Now I'm wondering if I overlooked mine?

Hole in the K is around .940 so that matches the stock pin size and when it is installed the pin tightens up on the taper and not against the shoulder. Real close to the shoulder though.

So to rephrase my question. If anyone has an LCA laying around, please measure the pin diameter near the shoulder like my photo above. Thank you

.923

Thank you hemi71x. With micrometer cannot get close to shoulder, so midway along taper my stock one matches yours at .920".

The pins in these aftermarket arms are .020" smaller for some dang reason (.905 or so).

Just a final note on this subject:
Interesting how 2 aftermarket parts could differ so much. Proforged pivot shaft 120-10050 on the left engages on the taper surface in the K member - same as OEM. QA1 lower control arm pivot shaft on the right fits in the K member up to the shoulder. Taper doesn't touch.