The Julius Keilwerth company became one of the largest saxophone manufacturers in Europe by the start of WWII, with approximately 150 workers.

Other significant complete-horn Keilwerth stencils include:- Note: some saxophones (e.g., Voss, Roxy, Senator, and De Villiers etc.)

that appear to have been made by Keilwerth were in fact manufactured by another German company called Dörfler & Jörka (also based in Nauheim) between 1949 and 1968.

The design and location of the neck screw (which is completely different from the type used by Keilwerth) is a simple but accurate method of identifying Dörfler & Jörka instruments.

By the end of the 1980s, Keilwerth had introduced its SX90R series saxophones and gained endorsements from jazz musicians such as Branford Marsalis, Courtney Pine, Ernie Watts, Don Wise, James Moody, Ron Holloway, Mike Smith,Grover Washington, Jr.[3]and David Liebman.

In 2013 Keilwerth introduced the MKX professional alto and tenor saxophones with a smaller bore for a more focused sound.