After discovering one of my locos would not fit under a bridge on my layout I made up a simple height and width jig to test clearances. I cut a profile corresponding to the maximum height and width required from a piece of 9mm ply and fixed this to a piece of wood which fits snugly in a suitable bogie wagon which is as long as expected on the layout. I left the bottom of the profile quite low as this would check for any low level obstructions that would get in the way of my transporter wagons. Following feedback I have added two more profile sections at the ends of the wagon so it will highlight issues on the far corners of curves as well as the inside edge. The outer section of ply can be used to check any future locos and rolling stock.