Metric Square Hole Steel Fender Washers are specifically designed to be used with Carriage Bolts and fasteners with square shafts.
The square hole design provides a tight fit against the square collar of the carriage bolt and prevents it from rotating.
A2 Stainless is corrosion resistant in damp environments. For marine applications, A4 / 316 Square Hole Washers are available as bulk box special orders.