Doorsteekvierkant 12,5 = 1⁄2 buiten-vierkant - voor 5121CT v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v. v....