From Factory RC:
Yokomo Yz2 gear box shim set allows 1mm and 2mm adjustments to the gear box height allowing for both the CG and dog bone plunge angle to change on the car. For carpet the team often runs the gear box shimmed up 2mm while using the YOKZ2-304C-2 and YOKZ2-018-2 pieces. This shim set can also be used without these parts on dirt/clay tracks to increase rear grip on those services that need it. Compatible with EVERY version of the Yz2 including the 1st Gen, CA, DT, and DTM. The addition of the water fall shim prevents bind up in the transmission assembly allowing for additional flex and grip.
Set includes both 1mm and 2mm shims for the gear box, rear “CA” style brace, and waterfall shims all made in carbon look plate. 1mm or 2mm ball stud washers are used on the rear DTM mount for adjusting height.
These were used in various cars at the recent IOC race in Las Vegas including Randy Pike’s helping him set the fastest laps in the 2wd Stock Buggy division during the event.