A modular tool holder for use separately and with one or more corresponding tool holders for attachment to an underlying metallic attachment surface, the modular tool holder comprising: a body portion (110; 210; 310; 410; 510; 610; 710; 810) comprising a base portion and a tool holding portion (140; 240; 340; 440; 540; 640; 740; 840) disposed above the base portion for receiving and holding a tool; at least one tongue (120; 220, 320; 420; 520; 620; 720; 820) disposed at a first side of the body portion; at least one tongue receiving groove (130; 230; 330; 430; 530; 630; 730; 830) disposed on a second side of the body portion opposite from the first side of the body portion; a metallic base plate positioned in the base portion of the body portion (110; 210; 310; 410; 510; 610; 710; 810) at an elevation beneath and aligned under the tool holding portion (140; 240; 340; 440; 540; 640; 740; 840); characterized by at least one magnet (150; 250; 350; 450; 550; 650; 750; 850) affixed to the underside of the metallic base plate to magnetically connect the modular tool holder to the metallic attachment surface, whereby the at least one magnet (150; 250; 350; 450; 550; 650; 750; 850) is disposed between the metallic base plate located above the at least one magnet and the metallic attachment surface located beneath the at least one magnet; and whereby the metallic baseplate enhancing the magnetic attraction of the modular tool holder to the metallic attachment surface relative to the use of the at least one magnet without the metallic base plate; further comprising a retainer to surround the at least one magnet (150; 250; 350; 450; 550; 650; 750; 850) to assist in retaining the at least one magnet in stationary position. a body portion (110; 210; 310; 410; 510; 610; 710; 810) comprising a base portion and a tool holding portion (140; 240; 340; 440; 540; 640; 740; 840) disposed above the base portion for receiving and holding a tool; at least one tongue (120; 220, 320; 420; 520; 620; 720; 820) disposed at a first side of the body portion; at least one tongue receiving groove (130; 230; 330; 430; 530; 630; 730; 830) disposed on a second side of the body portion opposite from the first side of the body portion; a metallic base plate positioned in the base portion of the body portion (110; 210; 310; 410; 510; 610; 710; 810) at an elevation beneath and aligned under the tool holding portion (140; 240; 340; 440; 540; 640; 740; 840); characterized by at least one magnet (150; 250; 350; 450; 550; 650; 750; 850) affixed to the underside of the metallic base plate to magnetically connect the modular tool holder to the metallic attachment surface, whereby the at least one magnet (150; 250; 350; 450; 550; 650; 750; 850) is disposed between the metallic base plate located above the at least one magnet and the metallic attachment surface located beneath the at least one magnet; and whereby the metallic baseplate enhancing the magnetic attraction of the modular tool holder to the metallic attachment surface relative to the use of the at least one magnet without the metallic base plate; further comprising a retainer to surround the at least one magnet (150; 250; 350; 450; 550; 650; 750; 850) to assist in retaining the at least one magnet in stationary position.