This is a pack of two 10x15x4mm rubber sealed “Speed” wheel bearings. ProTek R/C “Speed” bearings are high quality steel/chrome bearings designed for the R/C racing enthusiast.
These 10x15x4 rubber sealed bearings are the standard bearing for Xray hubs and 1/8th scale on-road hubs. Please check the manual that came with your vehicle for the correct size if you are not certain.
These are also used for diff outdrive bearings on the Kyosho Lazer ZX-5 1/10th scale 4WD electric buggy.
ProTek R/C is an AMain Sports & Hobbies brand.