Transition Strips are used when traversing from Mainline roadbed to Branchline/Siding roadbed, or vice-versa. Scale dimensions are 18" at one end and 12" at the other. The scale dimensions are 12'-9" across the top and 14'-9" across the bottom. Actual dimensions are 6.3 cm across the top (approx. 2-7/16" ), 8.3 cm across the bottom (3-1/4") and 21-1/2" long. There are 2 transition strips for each unit ordered.