Bolt blog 101
Today’s topic: Thread Types and Sizes
The most common thread sizes in bolts you come across are in 3 categories. Imperial, metric and whitworth. As a rule imperial is used mostly on American and canadian equipment. Metric (becoming the standard on everything))LIke??) on Japanese and whitworth on British(British what? Could mean anything you need to specify otherwsie there are too many holes). Im confused again i dont understand this bit why are they named different? Are they on particular brands?
BSW
British standard whitworth, becoming obsolete now, thank god.(WHY? Are they shit, give a reason why, the problems they have)
Started in 1841, up until then most threads had been made in house and without and standards. Pretty much a free for all. This thread was initially adopted by the Navy and soon spread to become the British standard. Nowadays it is hard to find and also a hard thread to cut for machinists. It uses a 55 degree angle of the thread and has the tops of the threads machined off to provide clearance for the nut or female thread. The most common use for BSW now is spring u bolts on small trailers. (IS there anything these are used for that nothing else will fit or is there an alternative?)
(CAN you add something about angle of thread and its significance?)
Imperial
Unified National Threads (UNC, UNF,UNEF and UNS) – adopted as the standard until 1948.
UN threaded bolts are all measured by the diameter first then their teeth per inch (TPI). TPI means how many peaks you can count in 1 inch of thread. For example ½-13 UNC will ½ inch outside diameter and have 13 threads per inch of thread whereas ½-20 UNF will have 20 threads per inch. Pretty simple but what significance does this have……
Metric
Metric bolts have been in use since the late 1800 as well. They use the same 60 degree thread angle (THIS isn’t stated under the UN heading , do you want it in there? Is it important enough for a explanation?) as UN bolts but use metric sizing for the outside diameter of the bolt.(It says the UN bolts use an outside diameter too) They also measure their pitch (? whats pitch?, is that TPI?) slightly differently, instead of counting threads per inch, metric fasteners measure the distance between two peaks of the threads. For example an M12 x 1.5mm COMMONLY used in?)bolt will have a 12mm diameter and 1.5mm between the peaks of the thread.
Imperial bolts threads (WHAT is a bolts threads?) originated in the US around the 1870’s and became a standard thread when suppliers received government contracts (CONTRACTS for what?). In the early 1900’s the US and Canada adopted a standard which included UNC UNF UNEF NPT. (WHAT DOES THIS MEAN??? You need to have long form at least once then you can abbreviate)
THREADs 101
Stainless steel – imperial UNC and UNF
When it comes to threads, basically the finer the thread the more load you can apply to that fastener before it will fail.
Imperial commonly has 2 types, UNC and UNF. There are others like UNS and UNEF. Today we will cover the 2 most common. UNC is definitely the most common and will perform best in most non critical situations.
(diagram here)
UNF is a fine thread, it has more more threads per inch and is used for high torque applications required on the bolt where you need reliability and as secure torque. (Story, this is why alot of cylinder head bolts you find are all fine thread, they need to be torqued up to an accurate level and stay tight) will happen if it doesn’t stay tight) Fine threads can be tightened up more than coarse threads because there is more surface area that is in contact with each other when the bolt is threaded into the nut or threaded hole. For example clamping load on a ½ unf bolt is around 14400 lbs whereas clamping load on a ½ unc bolt is 12700, around a 20% difference when using a finer
UNC is the standard.
Metric Fasteners
Metric fasteners are measured by pitch, Pitch is the distance between peaks on thread for example m10 bolt 10 mm diameter x 1mm pitch imm between peaks therefore would be finer than say a 1.5mm pitch.
Diagram.
Metric fasteners work on the same principal as imperial whereby the finer the pitch the more load you can place on the fastener.
Metric fasteners come in many different pitches, the most common are listed below.
Fine thread common uses,
Coarse threads common use