First - balls that haven't changed!Back in 2015 with the inclusion of the ST24, ST24M and ST24L (replacing AT21 on the top of the car) within the A700 Evo II, A700 Evo IIC and A700L2 kits there has been some confusion at build time about the proper ball studs to use. Without a caliper, the picture below will explain everything you need to know by analyzing the ball stud shoulder.
From left to right - ST24L, ST24 and ST03
Note the angle and thickness of the ball on the stud.
Second - bring out the new pivot balls!
During 2017 and 2018 a lot of variety of lower arm pivot balls have been created. Most of them are designed to either increase arm width or provide arm sweep. All in all -- this is still confusing to folks, so hopefully this clears things up.
- AT21 - the original pivot ball - now the "in kit" default for lower arms
- AT21S - the 0.5mm lower pivot ball - every useful in high grip, black carpet environments
- AT21S0.5 - a offset 0.5mm lower pivot ball - allows for 1) arm sweep; 2) width increase; 3) wheelbase adjustment - the tricky part is getting the balls aligned correctly
- AT21ST-A- steel version of AT21S that also includes a 2mm driver hole on top. this part will replace AT21S in the near future