Thread Pitch Gauge Tool - Why You Need It

Why You Need A Thread Pitch Gauge


How can a thread pitch gauge save you time and money when ordering British motorcycle parts? Let us explain. First off if you do not know what a thread pitch gauge is, a thread pitch gauge is a hand tool that allows you to measure a bolt or screws thread count per every inch. A thread pitch gauge usually comes in an assortment to allow you measure threads ranging from 10 T.P.I through 80 T.P.I. for example. Gauges come in many types to suit American thread forms, British, and even metric. The term T.P.I is short for "threads per inch". If you measure a bolt and it reads 26 T.P.I., that would mean that the bolt has a 26 threads per inch count.



Thread Pitch Gauge Tool

Pictured above is my trusty 1960's thread pitch gauge made by "Union Tool Co".


When working on a British motorcycle (or any motorcycle), there are always some tools that you just have to have, a thread pitch gauge is one of them. Mainly because it is handy, and it is universal. As we all know British motorcycles which include Triumph, BSA, Norton, Matchless, etc, all have many different types of thread forms. It is not uncommon to see BSF, UNF, UNC, & CEI thread forms all on one British bike! Not to forget that the spark plug holes are metric... You typically see this on 1968 and later models when Triumph and BSA motorcycles where starting to introduce American threads.



Measuring A Bolt On A Triumph Motorcycle Picture

Using the thread pitch gauge to measure a Triumph 650 crankcase bolt. Gauge states that this bolt has a thread pitch of 22 T.P.I.


Now to saving time and money. We have found that many times when ordering bolts, nuts, screws, studs, and anything with threads on it often times have been changed. For example, you own a 1970 Triumph T120R, you need the front axle nut. You call your local supplier (Classic British Spares of course) and you give us the part number that you need. We send you the nut. You attempt to install it but it will not thread because the thread pitch is wrong. Why? A previous owner installed an early axle with a different thread pitch. How would one know that? A thread pitch gauge. Basically a thread pitch gauge takes the time out of "assuming". Regardless if a motorcycle is all "original", when ever I have to replace anything that has threads on it, I get my thread pitch gauge out and measure first. We get calls throughout the month from customers buying 2 of everything because they are not sure if they have a UNF or CEI thread pitch. That could easily be avoided with a gauge. Ive seen gauges go from 10-50 dollars.



Although I do not stock any thread pitch gauges, they can be found locally at most fine autoparts store. If you cannot find it at your local store, you can find a thread pitch gauge here on the internet. I keep a thread pitch gauge on my desk and in my toolbox at all times. It is arguably one the most used hand tools that I use. I cannot stress enough of how important and handy this little tool is.


  • Classic British Spares

    @Glen I have never seen any metric hardware on a British machine other then the spark holes. The fork leg cap holes are notorious for getting stripped out. It’s very possible someone use a metric tap or simply wedged in a metric bolt. It should be a 24 TPI bolt for models 1969 & On. Thanks reading the post today!

  • Glen

    I wanted to replace the fork pinch bolts on my ’70 BSA A65T. I have a pitch gauge and could not find the proper fit. I believe the pitch to fall between 20 and 24 tpi but there was not a perfect fit. This bike was built late in the ’70 model year and possibly metric bolts were used. Any way, I just bought new bolts and nuts and solved the problem that way.

  • Classic British Spares

    @Scott Werner Thanks Scott for reading. Your right TPI is still TPI regardless of how old the tool is :)

  • Classic British Spares

    @Dave I understand what you are referring to. Your position is one of the main reasons why I wrote the blog. A thread pitch gauge is a life saver! Thanks for reading today!

  • Dave

    I sure could have used a thread guage for my 1968 BSA 441 Victor Special. I ordered some UNF stainless steel allen head bolts for the bike’s side cases from an English supplier and when I received them, they wouldn’t screw into the cases. It turns out they were CEI threads, not UNF because as they told me, the bike was probably built late ‘67 or early ’68. It’s not worth sending the bolts back to England so I had to buy another set that were CEI. Basically I paid double for those bolts. Sheesh!
    I’m off to my tool supplier today to buy a thread pitch guage!

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