This is a black Sorbo (hard foam\rubber like material) petrol tank chinpad, of the type seen fitted to Norton race bikes (and other makes) in many period photographs, and is ideal for fitting to Norton Racing International and Manx petrol tanks which are fitted with chinpad fittings.
We spent a long time hunting down a supplier of the correct 'look and feel' material, which is a dense black like rubber sorbo material of approximately 30mm (just over one inch) depth. The pads are cut to a suitable length and width for Norton chinpad petrol tanks, and as a final touch after cutting - the chinpads are linished on their side to clean up the cut faces and radius each corner, to give a much better look when fitted to a tank.
These pads are (approximately): 7 1/8" long x 4 1/4" wide.
I use the same black foam chinpad and straps on my own Big Plunger Manx Norton (shown in the photo) and other Manx tanked bikes.
Note we also sell the chinpad tabs and straps in this same section. To make the individual straps, cut 2 suitable lengths, then feed each end through the eyes of the chinpad tabs and then double back enough material to allow each end to be glued together using a suitable contact adhesive - I use Evo Stick 501. I allowed for an approximate 4" area of rubber on each end to be glued together, to ensure when attached to the tank they would not pull loose. The finished straps look just right with the chinpads clips and the sponge chinpad - see the photo of my own pre-war Manx that uses these straps.