Custom Kraft was the house brand of St. Louis Music Supply, a Missouri-based wholesaler and distributor. The name was first used commercially in 1938 on guitars sourced from the Harmony Company of Chicago, and was relaunched in 1961 as a full line of electric and acoustic instruments built by Kay and Valco. The brand's catalog spanned flattop and archtop acoustics, semi-hollow and solidbody electrics, basses, and tube amplifiers, all sold through department stores, catalogs, and independent music shops across the United States.

Among the better-known models are the Ambassador, a solidbody double-cutaway electric introduced in 1963 and generally attributed to Valco, and the Model 6116, a ladder-braced parlor acoustic built by Kay. In October 1968, St. Louis Music introduced its final Custom Kraft models — the Mod line — which included the Super Zapp six-string, the Saturator 12-string, and the Bone Buzzer bass. Production effectively ended when the combined Kay/Valco operation shut down in August 1968, though remaining stock continued to be offered into the early 1970s.

Custom Kraft instruments are now considered vintage department-store guitars, collected for their quirky mid-century styling, Valco and Kay pedigree, and distinctive pickups. They occupy a similar niche to other U.S. catalog brands of the period such as Silvertone, Airline, and Old Kraftsman.

Custom Kraft has 6 products cataloged on Equipboard, including Solid Body Electric Guitars, Hollowbody Electric Guitars, and Semi-Hollowbody Electric Guitars. Their gear is featured by 5 artists, with the strongest followings in Rock, Folk, World, & Country, and Pop. Notable users include Dan Auerbach, Ryan Adams, and David Roback.