Saturday, August 8, 2015
How to identify threads for pressure washer couplers and other mechanical things
Thread Types
Male and Female :
Male threads have the bumps on the outsideFemale threads have the bumps on the inside
BSP or Metric ?
The common threads on Pressure Washers are either BSP (British Standard Pipe) or Metric (prefixed M)BSP Threads
Common BSP threads used on pressure washers are 1/4, 3/8, 1/2 and 3/4. The annoying thing about BSP threads is that the tread type is not the fitting diameter, ie 3/4 BSP male thread does not measure 3/4 " diameter "Metric Threads
Metric threads are the same diameter as the thread size so an M14 does measure 14mm in diameter (but so does 1/4 inch BSP)
What is Pitch ?
So now we know that both a metric and imperial (BSP or M) can be the same width (diameter). If measuring the width does not define the thread, what does ? Pitch is the distance from the peak of one bumpy bit to the peak of the next. You can buy pitch guide tool that look a bit like tiny saws. You position each of the guides onto your thread until one matches exactly (a bit like a jigsaw). You can then read the pitch off the side of the pitch guide tool.
Note: Pitch is sometimes also quoted as TPI on BSP threads (teeth per inch)
M14x1.5 thread would be 14mm wide and have a pitch also in metric so 1.5 teeth (bumps) per millimetre.
MARYLAND METRICS -- THREAD IDENTIFICATION CHART SECTION (A): THREAD GUIDE
Note: Pitch is sometimes also quoted as TPI on BSP threads (teeth per inch)
M14x1.5 thread would be 14mm wide and have a pitch also in metric so 1.5 teeth (bumps) per millimetre.
MARYLAND METRICS -- THREAD IDENTIFICATION CHART SECTION (A): THREAD GUIDE
Swagelock the hydraulic fitting manufacturer made a great video for thread identification :
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