M-Wave Bike Seatpost Clamp with Rack Mounts - Universal Bicycle Rack Attachment for Commuting, Touring & Cargo Bikes

This does exactly what I wanted to do. It's strong and fit perfectly. I saw some bad reviews about people feeling like they didn't get the proper size. Please be aware that your seatpost size IS NOT the size to get for this clamp. If you can't find your seatpost clamp size online, contact the manufacturer to ask. My seatpost is something like 27.6mm, but the clamp I needed to get was 31.8mm. As soon as I got it in the mail I checked the size and it was a perfect fit. The only other thing to consider is if your bike frame is designed and rated to handle the abuse of a rear rack and cargo. Sometimes the bike doesn't have the eyelets because it's not meant to carry cargo, so if you're not sure, contact your bike manufacturer to ask. Trek was happy to help me, and it only took a out 5 minutes to get all the info I needed to feel safe getting this and putting a rack on.In case anyone is wondering, I put this on a 2023 Trek FX Sport 6, which is a full carbon fiber frame hybrid bike that is meant to handle moderate gravel and trails. It has eyelets lower on the frame near the cassette for a rack but not on the frame near the seatpost where you'd usually have eyelets for a rear rack, so this product was exactly what I needed.