圈上大峰 Basic Terminology3 ·External Threads(外螺纹) >the threads on a screw ·Internal Threads(内螺纹) >the threads on a nut ·Engagement Length,L。(旋合长度) >length over which the nut and the screw are engaged. 圈上大峰 Multiple Screw Threads2(多线螺纹) .Screws can be multiple-threaded by having two or more threads cut beside each other Double-threaded screw(双线螺纹) >lead is equal to twice the pitch,/=2p ,Triple-threaded screw(三线螺纹) >lead is equal to 3 times the pitch,/=3p .Advantage of multiple threads:They have >Smaller thread height >Increased lead for fast advancement of nut. .Standardized products all have single thread 1817 Basic Terminology3 • External Threads（外螺纹） the threads on a screw • Internal Threads（内螺纹） the threads on a nut • Engagement Length, Le （旋合长度） length over which the nut and the screw are engaged. 18 Multiple Screw Threads2（多线螺纹） •Screws can be multiple-threaded by having two or more threads cut beside each other •Double-threaded screw（双线螺纹） lead is equal to twice the pitch，l=2p •Triple-threaded screw （三线螺纹） lead is equal to 3 times the pitch, l=3p •Advantage of multiple threads: They have Smaller thread height Increased lead for fast advancement of nut. •Standardized products all have single thread