Originally Posted by Scottrik

If you look at an AE 1/12 lower arm at you'll notice there is a chamfer/countersink in the arm for the 8-32 mounting screws. Read the above post to see how the lack of same CAN affect (certainly not will) how the arm sits on the chassis plate when it is tightened down.

Now look at an IRS "lowered" AE arm. IRS mill .060" (ish) from the molded AE arm mount so it can move the arm itself closer to the track so you can use smaller tires. If you look at the 8-32 mounting hole you will see that the chamfer/countersink is removed when that material is removed. That factoid is how I tell standard AE arms from "lowered" IRS arms at a glance.

It sounds like the new IRS "reversible" arms maybe also lack this chamfer/countersink. Not a problem as it is certainly easy to add on your own.

Scottrik