Wrench sizes are given in either standard (SAE) or metric sizes. SAE wrench sizes vary from 5/32” to 2 1/2”, while metric sizes are from 4mm to 63mm. In SAE, the most commonly used ones are 3/8”, 1/2" and 1/4". In metric sizes, the most used ones are those between 7mm and 19mm. These are the usual sizes of nuts and bolts in most cars and equipment. If you’d be doing heavy-duty work, though, you may want to have bigger sizes as well.