Nylon jaws, no spring, box jointThese are a very high quality plier. Max Recommended Wire Thickness (*See Notes Above): Stainless and Titanium (SS/TI): Not recommendedCopper (CU): Not recommendedBronze and Brass (BZ/BJR): Not recommendedAluminum (anodized AA and bright AB): 12g Minimum Recommended Size (*See Notes Above): 18g