The scriber doubles up to do the flat unders and overs, then unscrewing and turning the base plate round to do the recess part of scribing the edges and corners.
The combination bar scriber has a brass locking centre knurled nut.
Very good quality tool. Comes with 3 scriber pins & 3 cutting blades stored in the handle compartment.
Length: 170 mm Width: 12 mm