Adding a stretch to your GROM? You'll need to buy a longer chain (132-ish links) to have a long enough chain, and then you use this tool to shorten it a bitto the exact length you need depending on the stretch length you choose... This is a very good tool from one of the best moto-specific tool manufacturers in the business, Motion Pro! I've been using this one here at the shop for a LONG time! Simple, inexpensive, and effective!