The carriage rollers are made from two bearing sleeves and a single R4ZZ bearing. You'll need to install two sleeves on each of the 12 bearings included in the kit.

Start by laying a sleeve half on the table, face up. Set an R4ZZ bearing into it and firmly press it into place.

Set another sleeve half on the table and press the R4ZZ bearing and sleeve into the new sleeve half to complete the carriage wheel.

Note that the sleeves have a sharp edge to them where they were cut free from the bulk stock during manufacture. Take special care not to injure yourself on this edge. It can easily be removed with a razor knife if you so choose.