There are two small front wheels for your carriage plate that help it travel smoothly and precisely. If one of yours becomes damaged, you can replace it with just a 3mm hex key.
Comes with 1 V-wheel. This is an original part directly from Glowforge (Not 3d printed.) 
Instructions on how to replace are here: https://support.glowforge.com/hc/en-us/articles/360055799153-Replace-the-Front-Carriage-Plate-V-Wheels
Part #: GF-ASM-01376-XP