The Nissan SR20 GTiR Head takes a plain 6.0mm id cap shim on one side, and a Rocker Guide cap shim on the other side of the rocker arm.
The Nissan SR20 GTR Head Takes a 10.0mm dia flat shim on one side, and a flat bottom Rocker Guide shim on the other side of the rocker arm
The Nissan SR20 VE Head Takes 10.0mm dia Flat shims on both sides of the rocker arm.