Quick Slicks TS44 tires are designed specifically for Thunder Slot (stock) wheels with 2 ribs. They will also fit RevoSlot cars with the wider rear wheels (refer to table below).
Multiple silicone compounds are available - this is the X-FIRM compound (part number: TS44XF).
Outer Diameter (O.D.): .803" (20.40mm)
Width (Contact Patch): .390" (9.90mm)