The original EZ wheels from Brompton are made of plastic with a spacer as the center core. It’s attached to the frame or rack with 35mm M5 screws. There’s no ball bearing therefore creating a lot of friction when rolling and that’s why almost every owner upgrade the EZ wheel on the first day.
There are many different types of aftermarket EZ wheels, ranging from SGD $15 all the way to few hundred ! No kidding, check out this beautiful Koeing Hanami with a hefty price tag. I got the OEM classic biscuit EZ wheel from Taobao about SGD$18 per pair. Remember to get the 58mm, I tried the 46mm and it’s too small to keep it the bike above the ground. You will need a M5 25mm screw, 2 nuts and 2 washers on each wheel, this is the order of how I install the wheel. Result in smooth rolling, easy to push the bicycle around when folded and very affordable modification.