How to Determine Screw Size Thread Count Step 1. Lay the screw down on a flat surface. Step 2. Place a steel rule down the axis of the screw . Step 3. Count the number of thread gaps within 1 inch of the screw . Step 4. Divide the count of thread gaps into the length . Step 5. M2.5 Screws . For instance if you are measuring an M2x5 pan head screw the overall length will be 6.60mm but it will be listed under the M2x5 because a pan head is measured from underneath the head where as a standard flat head screw takes its size from the measurement … How to Measure Fastener Length . Fastener length is measured from where the material surface is assumed to be, to. the end of the fastener. For fasteners where the head usually. sits above the surface, the. measurement is from directly under. the head to the end of the fastener.

Dec 30, 2006 Note, however, that a flathead screw, designed to sit flush in a countersunk material, is measured to the top of the head. For unified threads, the length is given in inches. A 1/ 4-20 x 3 /4 screw is .75 inches (1.9 cm) long. The length may be given in fractional inches or the decimal equivalent. Steps to Choosing the Correct Screw: Select a style. heree in a variety of styles — flat head, Phillips, square and torque. Square and torque heads make it easier to keep your drill bits in place and prevent slipping and stripping. Select a screw size. Sheet Metal Screws . Sheet metal screw measurement depends upon the type of screw you are using. Countersunk screws (Flat or Oval head) are measured by overall length . Pan Head, truss head, and Hex Head screws are measured from under the head.