Hi every body i hope i post in the right place:) i have a problem i’m interresting about a lot of vex pieces, but i don’t want to use a vex kit, so know what i can or can’t do with vex whheels i have to know wha’ts the bore diameter in vex wheels??? i searched a lot but nothing!!! so if someone have a vex wheel and a caliper it will be nice to give me this information about vex developpement kit 
thanks a lot! and sorry for my poor english!
Hi victorjung,
Welcome to the RobotShop Forum. You have come to the right place. The VEX kits do not use standard round shafts and instead use only square shafts which are 0.125" (3.175mm, with rounded corners). The VEX wheels also have this square bore (not round), making them harder to use with parts from other manufacturers.
Hope this helps,