<P> While saws for cutting metal had been in use for many years, significant improvements in longevity and efficiency were made in the 1880s by Max Flower - Nash . Clemson, a founder of Clemson Bros., Inc of Middletown, New York, United States, . Clemson conducted tests which involved changing the dimensions, shapes of teeth, styles of set, and variable heat treatments of blades . Clemson claimed enormous improvements to the cutting ability of blades and built a major industrial operation manufacturing hacksaw blades sold under the trade name Star Hack Saw . In 1898, Clemson was granted US Patent 601947, which details various improvements in the hacksaw . </P> <P> Standard hacksaw blade lengths are 10 to 12 in (250 to 300 mm). Blades can be as small as 6 in (150 mm). Powered hacksaws may use large blades in a range of sizes, or small machines may use the same hand blades . </P> <P> The pitch of the teeth can be from fourteen to thirty - two teeth per inch (TPI) for a hand blade, with as few as three TPI for a large power hacksaw blade . The blade chosen is based on the thickness of the material being cut, with a minimum of three teeth in the material . As hacksaw teeth are so small, they are set in a "wave" set . As for other saws they are set from side to side to provide a kerf or clearance when sawing, but the set of a hacksaw changes gradually from tooth to tooth in a smooth curve, rather than alternate teeth set left and right . </P> <P> Hacksaw blades are normally quite brittle, so care needs to be taken to prevent brittle fracture of the blade . Early blades were of carbon steel, now termed' low alloy' blades, and were relatively soft and flexible . They avoided breakage, but also wore out rapidly . Except where cost is a particular concern, this type is now obsolete .' Low alloy' blades are still the only type available for the Junior hacksaw, which limits the usefulness of this otherwise popular saw . </P>

What determines the number of teeth to use on a hacksaw