I just received a new thumb throttle attachment for my Radrunner1, although it can fit some other Rad power bike models. I just wanted to share my relief and excitement here if any of you have my wrist issues. I admit, I was skeptical....BUT this thumb throttle attachment is AWESOME! I have a RadRunner1. I have some arthritis in my wrists and even with light throttle usage for a boost here and there, my wrist bugs me at the end of the day. This throttle fits like a GLOVE! I cleaned off my grip with an alcohol swab first to remove any hand oils. It went on easily, and fits very snugly, without any slippage on my initial two rides! I love the fact that there is still a little room to use the throttle the traditional way if you desire. ( I love options.) I placed it in a slightly downward position, so I don't bump it when I am at a standstill, but you can place it where best for you. I got the orange, because I have bumped my throttle accidentally when stopped, and this calls my attention to the throttle to avoid an accidental bump. In addition, it matches my bikes orange accent colors. My husband has a RadRover, and now wants one in black. It comes in MANY colors! I found this on Etsy. I have no relationship with this business, other than as a satisfied customer. Seller is Etsy shop 3DPrintsbyTheodore. Here is the link: https://www.etsy.com/listing/1188254154/ebike-rad-power-throttle-thumb-throttle?click_key=71f1b1fa408d1ccce30fba0c04e4f725e5237520%3A1188254154&click_sum=342acebe&ref=hp_rf-1