Fastener Express has a variety of flange screws for all your project needs. Flange screws are designed with a washer built on under the cap. This design spreads the fastening weight load over a wider area for stability and strength. Like a loose washer, the built on one under the cap reduces slippage and increases the longevity of the connection. Some caps have ridges as well, which dig into the drilling surface and prohibit turning once the screw is set.