Next to that are two extrusions which will allow me to install two pegs (https://www.dashboardpws.com/shop/spirail-dogs). These pegs support workpieces that are clamped to the side of the bench. So if I have a 24" wide panel, I can set the pegs to 20" (using the tape you see) and know that the panel will be 4" proud of the workbench top. I don't have to guess where the workpiece will be, I'll know precisely Normally one peg is enough but the tape also allows me to make sure that if I use two pegs, they will be very close to parallel (close enough anyway).