Those Nord-Locks are awesome and great for header bolt applications too. Places like Fastenal also has them.
https://www.fastenal.com/products/fasteners/washers/lock-washers/nord-lock-inc?r=~|categoryl1:%22600000%20Fasteners%22|~%20~|categoryl2:%22600089%20Washers%22|~%20~|categoryl3:%22600101%20Lock%20Washers%22|~%20~|manufacturer:^%22NORD-LOCK,%20INC.%22$|~