DEWHEL Aluminum Black Water Temp Meter Temperature Gauge Joint Pipe Radiator Sensor Adaptor Clamps 38mm

My opinion and experience with size selection (review at the end):You want a snug fit (a little resistance when attaching the hose). Measure the inside diameter of the section of the hose you will be splicing it into. If that isn’t an option because you’d have to cut the hose and you can’t have your car down for a couple of days, then measure the outside diameter and subtract the thickness of the hose wall X2. Based on the measured inside diameter of the hose, select the adapter that is the next size up ( 2mm). You may be able to get away without going slightly up in size, but the clamps will really have to bring it down and while it might not leak, the seal wouldn’t be the best. USE YOUR OWN DISCRETION this is my personal recommendation based on my experience:The ID of my radiator hose was approximately 31.7mm and at the very least you should round that number up, so I ordered a 32mm adapter. Upon fitting it, it was appropriately sized, but it wasn’t a snug fit and without clamps it would easily fall out. I was concerned about the seal because of how much you would have to tighten the clamps. I decided to order a 34mm and it worked out great. I could have easily used 36mm as well, but since my radiator hose was not new I left room to take into account that my old hose was probably expanded slightly. Great time to just replace the whole hose! Even though you may have to cut it depending on your application.Installation Review:Installation was easy. You will need to make a small grounding wire to attach from the small screw on the adapter to somewhere on the car frame or engine. If you have them, you may want to use hose clamps that are a little beefier than the clamps provided. I used this with an aftermarket Bosch water temp sensor and gauge, using Teflon tape on the sensor threads before installing it into the adapter. I cut out a small section of the upper radiator hose (hot side, using razor blade) to install the adapter. I would install it as close to the engine water outlet as you can. After installation be sure that none of the modified hose sits above the top of the radiator in order to help keep air from getting trapped in the system.One month after install:Everything is perfect. Great product.