Standard Cover Plate is 2 11/16" (maximum) wide x 6 1/4" long (on top) and is fastened with one (1) 6mm screw going through the front of the mast. Note: Older NG1 Fractional Rig Mastheads used different (non-compatible) Cover Plates, See NG1 Fractional Rig Masthead. NG-46 Masthead Sheave: NG1-3:. "/>