Thumbscrews have smooth-turning, diamond-knurled heads, while captive screws come with slotted heads. Shoulder screws are held to tight tolerance (+0.000/0.001 diameter, and +0.002/0.000 length) and come with slotted or socket heads. All screw types come in stainless steel as well as other materials and finishes. Keystone Electronics Corp., 31-07 20th Rd., Astoria, NY 11105, (718) 956-8900, www.keyelco.com