Sc-143 O-Ring Combination with Drop Curb2. 5 Ring with locked mouthpiece, rein ring, and drop curb. The headstall ring doesn't allow this combination to roll around on the ring. This bit is light but incredibly effective in providing support and balance as you increase with speed. This bit will square one up in the shoulders and help give a cue to finish the turns tight while adding speed. Great for schooling or competition.