I recently picked up a used scroll saw, and noticed an issue with the blade tension bolt. After disassembling (and partially reassembling) the saw, the problem became apparent. The threads on the stock bolt were stripped. To repair it, I used a piece of 1/4 - 20 all thread and a nut (you could use a long bolt). The top wedge bar was drilled and threaded to match the bolt. The bottom was drilled to allow it to move freely on the bolt. I managed to use the original handle. The original bolt is reversed thread, so this repair changes the direction in which you tighten or loosen the blade.

Remember to be safe and use the proper safety equipment when you are working with power tools.