Specifically designed to attach wood to metal (Max. 12mm). Metric thread with wings designed to ream out the timber, so the screw can achieve Max. R.P.M. without burning out. When the wings hit the metal they will break off to permit the thread to self-tap into the metal. Hardened carbon steel drill tip fused on to an A2-304 Austenitic Stainless Steel body" Thread Dia. mm: 5.5 Length mm: 55 Head Type: Countersunk with Ribs Recess Type: Phillips Point Type: Self-Drilling No.5 Material: Bi-Metal/A2-304 Stainless Steel/Carbon Steel Effective Thread Length mm: 24 Max Drilling Thickness mm: 12.0 To Suit Timber mm: 13Size 5.5 x 55 - 200 pcs Timco Metal Timber to Heavy Section Screws Countersunk Wing-Tip in Silver