Straw brooms are getting harder to come by these days, and other members of your household may not appreciate it if you destroy an otherwise useful straw broom just to satisfy your musical needs. Used broom wire tends to be slightly corroded and requires some cleanup with Nevr-Dul metal polish.
One String Willie is offering unused, standard tin-coated steel broom wire, 18-1/2 gauge (0.0445" +/- 0.001"), with a tensile strength of 135,000 psi. Each coil is 23-25 feet long, enough to make seven or so medium-sized diddley bows. To give a sense of the size of the coil, the card in the picture is the size of a standard (poker-sized) playing card.
Have any questions?
Contact the shop owner.

