Our Seatpost Clamps with rack mounts provide a stable spot to mount your rear rack stays to on bikes without seatstay braze-ons. Very handy. Also great for light mounts, a saddlebag stabilizer, or anything else you problem solving people tend to dream up. Unless you&';re thinking about towing a jet ski with it. Let&';s be reasonable.Tech Detailsa Available in 31.8 mm and 34.9 mm diametersa Alloy clampa Stainless steel bolta Threaded to accept standard M5 bolts