The Martin Tool Metric Check Nut Wrench - 18mm is made of drop forged steel and is available in fractional sizes from 1/2" to 1-11/16" and metric sizes from 10mm to 41mm. These industrial black wrenches are ideal for use on check nuts, stop nuts, jam nuts, and hydraulic fittings. The smaller sizes can also be used for servicing, and are known as Thin Head Wrenches. These specialized tools have a 15 degree angled slotted opening and are designed for adjusting and/or locking extremely thin nuts. Made in the U.S.A., these wrenches are of high quality and are coated with industrial black for durability.