Paul continued to suggest technical improvements, although they were not always successful commercially. In 1962, Paul was issued US Patent No. 3,018,680, for a pickup in which the coil was physically attached to the strings. In the mid-1940s, he introduced an aluminum guitar with the tuning mechanisms below the bridge. As it had no headstock, the string attachments were at the nut, it was the first "headless" guitar. Unfortunately, Paul's guitar was so sensitive to the heat from stage lights that it would not keep tune. However, he used it for several of his hit recordings. This style was further developed by others, most successfully Ned Steinberger.