They're the aluminum front side direct cups which were first included in the TRF420 chassis kit. Lightweight aluminum elements have actually a durable anodized finish.
Suitable Chassis
TA07 MS*1, TA07 PRO*1, TRF419*1, TRF419X*1, TRF419XR*1 & TRF420 Chassis
*1Use with Item 51642 TRF420 Front Direct Pulley (37T). Two 3x10mm hex screws are separately needed.
*The formal Tamiya R/C Parts Matching List has lots of details about framework compatible with Tamiya Spare and Hop-Up choice components.
