The will work with bumpers from Mardave, Kamtec and other popular manufactures including DDR Racing. See picture for an example of each colour.
Kyosho RC Helicopter Concept 30 H3310 Spacer Set (S)
Kondo Kagaku KXR Series Servo Arm Spacer Set | Kondo Science
Tamiya Mini 4WD 95442 Aluminum Spacer Set (12/6.7/6/3/1.5mm 2pcs. Each) Gold
Schumacher U7899 Diff Spacer Set - A2/3,E4-6,Icon/2 Rc Car
Tamiya 54367 Rear Tread Spacer Set RM01
KDS Agile 5.5 Screw Set KA-55-077
