I have to attach the clutch stoneguard/coverplate (C.5072) to my ’56 Mk1.
The engine/gearbox is in the car.
I just bought some 1/4" coarse Setscrews at the hardware store and cannot get it to thread into the holes.
The parts book specifies four CS.125/4D. I think that means: 1/4” coarse hex head setscrew, ½” long.
The XK 140 uses the same setscrew.
The Mk 2 uses a UCS.125/4R.
One of the fastener guides I have states that the “1” in the part number indicates a hex head, another guide says the “1” indicates ISO metric coarse.
Am I using the correct size setscrew or, should I be using a metric size?
I don’t know if the problem is with the setscrew I am using or a previous owner/mechanic cross threaded the housing threads.
Thanks
Bruce,
There is no ambiguity re the decoding system for Jaguar fasteners.
During WW2, the British Ministry of Supply contending with the war-time logistics problems, developed a coding system that was expected to be understood and adopted by British Industry, with some fixed parameters, but some flexibility. Jaguar voluntarily decided to adopt their version for their own internal use, and in essence took effect from the start of post-war Mark IV saloon production, and remained unchanged until a slight review in about 1957, so pretty well as of the XK150 onwards.
Your CS.125/4D decodes as follows:-
Cx. = UNC thread.
xS. = Setscrew.
.1xx = standard Hexagon Head (Standard as in dimensions prescribed in the British Standard re thickness and across-flats dimension)
.x25 = 1/4" diameter.
/4x = 4 x 1/8" long or 1/2" length.
/xD = “D” grade of steel, which was the basic mild steel 45-55 ton UTS steel. This ‘D’ was required to be shown on head of bolts/setscrews, albeit in c1953 the scale was changed, with the same 45-55 ton steel now called grade ‘R’, albeit Jaguar continued with the ‘D’ coding in paperwork up until the 1957 review.
So your CS.125/4D is a standard Hex-headed mild-steel 1/4"UNC x 1/2" long setscrew.
Your Mark 2 code UCS.125/4R is the identical Setscrew, except now uses the 1957 revised coding.
UC replaces just C, and still denotes Unified Coarse (UNC) thread.
/xR is the now up-to-date material grade for 45-55 ton UTS mild steel.
No idea where you got your ‘1’ = ISO Metric, but clearly ISO Metric has nothing to do with any Jaguar made in the 1950s/60s.
Yep, 1/4-20 UNC x 1/2" long hex head.
Common as dust here in the US.
What country are you in?
You might need to run a tap through the holes.
Thanks Rob, I’m in the US. Is coarse always equal to 20 TPI? I’ll have to check the threads with a gauge if there are other versions of coarse threaded 1/4" setscrew.
Thanks. The “1 = ISO Metric” came from at page at the Martin Robey website. In reviewing it again I see it is a scan of a British Leyland document from 2005 titled “BRITISH LEYLAND FASTENERS CODING SYSTEM.” I guess things have changed.
Yes, in the USA a 1/4" coarse thread screw will always be 20 Threads Per Inch.
Fine thread will be 28 TPI, but this is rarely used on aluminum parts.
Could you have bought 6mm metric by mistake?
There are also 1/4-20 British Standard Whitworth threads, but it would be almost unheard of to find such an animal in any US hardware store.