G1 Throttlebot Rollbar's head. Two sizes are available. X-Small is for Titans Return Brawn body. Small is for Combiner Wars Hound/Swindle figure.
Note for X-Small (TR): If printed in BHDA, the base of the head may be a bit too thick due to artifacts. Simply put the head on sanding paper and sand off a thin layer so that it can slide comfortably onto the neck.