Trip Arm for JACOBSON Hit Miss Engine. Trip arm is 10 1/2 long and has part no. 3122 cast into it. Igniter trip arm goes on the cap of the sideshaft. 1 3/8 diameter hole for the sideshaft. I apologize for any inconvenience. Please feel free to call me with questions. My parts inventory has grown out of control, so set a reminder to check back frequently for new listings! If you don’t see a part you need listed, good chance I just haven’t gotten around to it yet, so just check with me. Like I said, I have been doing this a long time and try to list everything accurately and to provide a detailed explanation of the item, both good and the bad. If you decide you don’t want it or find another one cheaper, I won’t take it back. For example, if my measurements are wrong I would take it back. Most of my parts are listed “AS IS” and are in unknown working condition, unless otherwise stated. Check out my other items. Be sure to add me to your favorites list. Be sure to check out my website for other engines and engine related items / gasenginetom.