Considering the size of the bellows, you want the heavy bellows cloth (0.044").

Gluing the cloth to the wood is not going to be an easy job. On a scale of 1-10 with 10 being the most difficult, the job is an 8 or a 9.

Back in the day, the manufacturer had a jig that (a) held the bellows open to the correct span while the cloth was being glued to the wood (b) applied pressure to all of the gluing surfaces like a C-clamp with three sides, and (c) help the cloth in the correct position during the gluing process.

Naturally, we don't have that luxury. So, what to do?

It's recommended that you pre-size the strip of cloth so that it won't have to be cut or trimmed after it is glued in place. Make sure you have at least a 2" overlap at the hinged end of the bellow. Dry fit the piece to make sure it will fit well. Naturally, you'll have to lay out the cloth and glue the stiffeners in place before you start gluing the cloth to the wood. As for the material to use for the stiffeners, I use the cardboard that's on the back of a large desk-type calendar.

Preparation:
1) Using a strip of heavy cloth, glue a strip of cloth across the outside edge of the hinged end of the bellows while the bellows is in the closed position. Let it dry thoroughly. (point A)

2) Using a threaded rod and Combination Mushroom Head Toggle Bolts and nuts, support the bellows in an open position to the correct span. (see diagram)

3) Using a strip of hardwood or metal that the same thickness and the same length as the wood that's glued to the main bellows board, cut the strip so that it is about 1/16" narrower than the flap of cloth that will be glued to the main board. (see diagram and picture) Put small pilot screw holes in the strip to secure the strip to the main board after the strip is glued in place.

4) If you're using animal hide glue (cold or hot), size all of the gluing surfaces with a thin coat of glue. If you're using a white or yellow glue, do not size the surfaces.

Gluing:

1) Glue the cloth strip to point 1 first. I recommend using small tacks or push pins to hold the cloth in place while it's drying. If you can use the jig that you made in step 3 of the preparations, that would be even better.

2) Glue the strip to point 2 next. (Use the jig) Let it dry.

3) Glue the cloth to the edges of the moveable board. (Use the jig) Let them dry.

4) Glue the cloth to the main board and squeeze out the excess glue with your fingers before using the jig to secure the edge of the strip to the main board.

5) Once everything is dry, remove the threaded rod, and collapse the bellow. Then glue the 2" overlaps to the cloth on the hinged end. Use tacks to hold them in place.