EML 2023 – Threads and Fasteners Lecture 1 - Nomenclature

Thread Terminology

Thread Callouts - Metric (mm) (mm) (mm)

Thread Callouts – ANSI Unified 1 – loosest fit 2 – normal fit 3 – most exact fit B represents internal thread (in) UNC – Unified National Course UNF – Unified National Fine UNEF – Unified National Extra Fine UN – Unified National

Thread Callouts – ANSI Unified Assumes course threads with a nominal fit (2). (in)

Goal: connect the top part to the bottom part using a #10-24 cap screw which has a head taper of 82˚ must determine length of screw

Steps: buy the screw drill a countersunk hole without threads (clearance hole) into the top part drill a threaded hole in the bottom part

2 things to know if you tap a hole the thread length should be at least twice the diameter of the fastener if you use a bolt to connect some bodies the bolt should extend beyond the nut by at least two thread pitches How long should the screw be?

the major diameter of the #10 screw is  .190” the length of the screw must be at least as long as .30” + 2.19” =.68 will purchase a #10-24 screw that is .75” long

The major diameter of the screw is .190”. What should the diameter of the clearance hole be?

http://www.engineershandbook.com/ Engineer’s Handbook

Was able to download a SolidWorks part file of this cap screw.

A clearance hole has been created for a #10 flat head screw with an 82˚ head taper.

A tapped hole for a #10-24 screw. The screw we selected is .75” long. Therefore the thread depth of the hole must be at least .75”-.3” = .45” deep. I selected a thread depth of 0.45” and a pilot hole depth of .66”.

If you only tap the blue body to the recommended depth of 2 major , i.e. .38”, you will have the following.

2nd Example Problem 3/8” – 24 cap screw blocks are 1.5”1.5”.50”

2 things to remember if you tap a hole the thread length should be at least twice the diameter of the fastener if you use a bolt to connect some bodies the bolt should extend beyond the nut by at least two thread pitches

Determining Bolt Length

Bolt length calculation Bolt must be 1.988” long plus the distance of 2 extra pitches. The bolt has 24 threads per inch. Two extra pitches will require an extra 1/12” of an inch. Total minimum length is 1.988+0.083 = 2.071” . Find the next longest available bolt. .50” 1.988” .08” 21/64”

2 things to remember if you tap a hole the thread length should be at least twice the diameter of the hole if you use a bolt to connect some bodies the bolt should extend beyond the nut by at least two thread pitches