Not to derail, but for those who have use the Herm Sprenger Duo, how have you found the sizing/fit to be? I’m looking to order the eggbutt for my mare, but the sizes are 5 1/8" (130mm) or 5 1/2" (140mm) whereas she’s a 5 1/4" in her current NS eggbutt (133mm).
ETA: I got my hands on a 5.5" Duo loose ring, and it measured slightly smaller than the 5.5" Duo eggbutt. The loose ring was also a little too small for her, so it looks like the 5.5" Duo eggbutt is going to be the best choice.
