This ring goes on the chamber mount.

Fits models: GB1M-IT, GB1P, GB2M5.5-IT, GB2P, GB3M-10-IT, GB3M-5.5-IT, GB3P, GB4M-IT, GB5M-IT, GB5MV-10-LD, GB6MP-10-LD-U, GB8MP-10-LD-U, GBK, GBLP, GBM, GBSKI, GBSuperSKI