a lot of suds will have a course thread one end and a fine thread the other dont ask me why i have know idea.
but most threads on these old cats are sae threads. an yes a couple of thread pitch guages one of each for metric, sae and whitworth along with a comprehensive tapping chart comes in handy. i have a very good guide book written by tubal cain covering drills and threads and it has a comprehensive selection of charts for various threads drills and conversions for drills even in letter sizes to metric and imperial.

I used to have a thread pitch gauge but I have not used it in years. I cant locate it right now so maybe I will buy another. I had never bothered to have a metric one, but I will probably buy both. My dad was a gunsmith so I still have box,s of tools that I have not sorted thru. Most are for much smaller stuff than Cat tools but lots of precision stuff.
Grant.

Anything Cat made that is in the antique class made in in USA is inch NC or NF in inches. When you get to European or Japanese manufactory probably metric. The closest to odd ball I know if is 9/16 which is a rather rare size in most USA made things.

Some of the plugs Cat used are also bolt threads rather than pipe as most old farmers are looking for.

yes all the old stuff actually made by or specifically for cat is sae threads. its after the early 80s that it might be a mixed bag. also beware of machine that are outside the U.S particularly countries that were British colonies as some stuff may have been changed as farmer engineering to whitworth or whatever was on hand i found a couple of those on our machine. the get it home or get the job finished fixes often become permanent. you say 9/16 is odd try 1/2 united nation special(its sort of in between unf and unc) ive only seen it used on one item.

trainzkid88 wrote:

 try 1/2 united nation special(its sort of in between unf and unc) ive only seen it used on one item.
 

 

By united nation special do you mean Unified National Special? Pretty sure any thing to do with the United Nations will be metric and under the ISO standard.
In regards to why studs usually have a coarser thread at one end, I will give you a hint, it has to do with what it is screwed into.

yes unified national. bloody typos. i believe its to do with course threads putting on large force and the way they lock compared to fine threads. i have seen studs threaded the same both ends but that was brass studs into aluminium alloy on a single cyl marine engine. coincidently the uns thread was on BSA stationary engine.

UNS is a rolled thread at 8TPI. At the power plant where I work we have hundreds of pipe flanges bolted together using UNS threaded bolts. Allowed the company building the plant to save money by using UNS studs as they can use the same thread rolling dies for all sizes of threads.

Course thread on studs has nothing to do with they way they lock, it is to do with the material the parent metal is made of. Studs have a course thread on one end for the same reason that you will rarely see a fine thread screwed in to a cast iron or alloy part. The thread is also usually longer than the fine end to allow more contact area between the softer cast iron and the bolt or stud.
I learnt this at Trade school (TAFE) both in my main trade as a fitter/machinist and as my secondary trade as a mechanic. I am also a fully qualified welder with pressure welding qualifications and a fully qualified plumber.

then you must have been a busy boy. or got bored easily. but you would always be able to get work somewhere.