What size wrench is used for an M8 bolt?
2 Answers
An M8 bolt requires an open-end wrench with a size of 14. For hex bolts, the corresponding open-end wrench size is more accurately determined by the hex nut, as there are both standard hex head bolts and small hex head bolts. Open-end wrench sizes: Common open-end wrench sizes are 7, 8, 10, 14, 17, 19, 22, 24, 27, 30, 32, 36, 41, 46, 55, and 65; corresponding to thread sizes M4, M5, M6, M8, M10, M12, M14, M16, M18, M20, M22, M24, M27, M30, M36, and M42. Units: Metric thread diameters are measured in millimeters, such as 6, 8, 10, 12, 18, 20 mm, etc. The thread pitch is also measured in millimeters, such as 0.5, 0.75, 1, 1.5, 2, 3, etc.
As a regular car owner who often does DIY repairs, I can tell you that the most commonly used wrench for an M8 bolt is a 13mm one. In cars, you'll frequently encounter M8 bolts in places like securing engine guards or small brackets. I remember last time when changing the oil filter, those small bolts were just right for a 13mm box-end wrench. Using the wrong size won't do—12mm is too small and won't fit, while 14mm is too big and can easily slip, damaging the bolt head, making repairs difficult later. I recommend keeping a complete set of metric wrenches; don't skimp and buy poor-quality tools, or you might slip and hurt yourself while tightening bolts. Car repairs require precision—bolts may be small but are crucial, and torque control is important to avoid over-tightening and snapping them. With a bit of practice, you'll get the hang of it. Having the right tools makes the job faster and safer, and keeping such equipment in your home garage makes emergency repairs much easier.
