It has the flexibility of being used with 3/8"D accessories or 1/2"D with the adaptor supplied. It can also be driven with a standard 21mm spanner. 3 jaw oil filter wrench. Specifically designed for motorcycles. Can be used with 3/8"D or 1/2"D with an adaptor. Jaws open from 45-75mm. It can also be driven with a standard 21mm spanner.