Can anyone tell me the thread size of the 3 setscrews that attach the Otter temp switch to the water elbow on the XK120, please? Part number is C7134/1.Thanks!
Chris
canāt check at the moment but given aluminum and generally its coarse threat for alluminiun your left with whitworth BSW sure some will have correct answer terry
Chris,
These 3 screws are 2BA with Hex head. The length will be around 1/2" but you better check the depth of the hole first.
Bob K.
Nope, mine are #10-24 UNC x 1/2" long hex head.
Round heads and pan heads with a slot are common here. Tough to find anymore with a hex head, but McMaster-Carr has 'em.
This illustrated configuration must have been standard on some models and a variation on othersā¦
In this instance, the Otter switch was screw-fastened to a brass insert attached/soldered? to the outlet elbow. The 3/16" screws, therefore, were fine-threaded (32), joining the brass, vice the aluminum portion of housing. I have a variety of the fine-threaded bolts used for this purpose. The heads are all 5/16" and have markings varying from dimples with the Letters āRā or āSā, plain dimples, and the standard āBEESā.
Some disagreement hereā¦ Iāll clean up the threads of the screw I took out on the rotary wire brush and measure it with a thread gauge and see what I come up with.
I looked on my thread chart and I see that 3/16 BSW is 24 tpi and #10-24 UNC is 3/16" dia, so it may be really hard to distinguish between the two without a magnifying glass.
But I have always understood that everything on the XK head and intake manifold except water ports was UNC threads because BSW/BSF had been declared obsolescent in 1947, encouraging manufacturers to go away from it and to UNC/UNF.
Wow, a lot of opinions all over the place 
The three Set Screws securing the THERMOSTAT (Otter Switch) to the Inlet Manifold are clearly identified as being C.7134/1 part number, thus are a ānon-standardā fastener given its own āC-prefixā part number rather than the ādecodeableā part number as given to all āstandardā fasteners, and āstandardā means a fastener complying with the prevailing British Standard where it exists as it does for various thread Setscrewsā¦
But in this case a C.7134/1 is only deemed ānon-standardā as it has additional Cadmium PLating of an otherwise āstandardā fastener that is a CS.119/4D which decodes according the system introduced during WW2 by the British Ministry of Supply as being a No.10 ANC Hex headed setscrew x 1/2" long made of grade āDā steel, which is a 45/55 ton mild steel. ANC = American National Course thread which is what the British referred to the National Course thread as then in use in USA, which was often also simply referred to as being S.A.E. thread. In the 1930s/40s there was no British Standard for any threads other than the family of Whitworth threads, most commonly BSW, BSF and BA, but also others such as BSC, BSPP, BSPT etc.
During WW2 due to field problems with shared British and American equipment, being serviced/repaired in British and/or American workshops the wise minds decided there was a need for standardisation, so a series of ABC Conferences (A = American, B= British representing interests of the British Commonwealth, and C = Canada) made several resolutions, one of which was the development of the Unified series of threads, later known as UNC, UNF, UNEF etc that then promoted each member country to work with their local industries to adopt the new Unified series of threads, and thus fasteners, and indeed spanners. Given we are interested in Jaguar primarily, Jaguar chose to rapidly adopt ANF/ANC threads/fasteners in advance of the development/introduction of British Standards for the new agreed Unified threads, and indeed the new Mark V and XK120 models saw the first partial use of ANC/ANF threads, in conjunction with outgoing BSW/BSF threads noting the first British Standard for UNF fasteners was not actually introduced until the issue of BS.1768 in September 1951. The British Government encouraged companies to export or bust, post-war, and although Jaguar quickly embraced the preliminary adoption of ANC/ANF from 1949 onwards, other manufacturers who supplied Jaguar with components were much slower to varying degrees, and indeed SU stayed with BSF/BA/BSW throughout the entire XK and E-type period, until eventially moving to Metric in the 1970s and never adopted Unified fasteners. So anyone with an XK needs to look at likely manufacturer/supplier as to likely threads/fasteners to be found, noting that the entire British Industry chose to remain with BA threads for small fasteners, as the UNEF thread simply was not wanted/likedā¦ thus any XK owner needs a set of BA spanners as well.
But these Cadmium plated, but otherwise standard CS.119/4D Setscrews - were No.10 ANC x 1/2in long and as before the D = the 45/55 ton grade of mild steel used, as Jaguar took the engineering carriage of threads they used in their own inlet manifolds that they machined up from castings supplied by both WYF and WM foundries. Now this gets further complicated by other initiatives, such as the 1951 introduction of the new UNified Standards, which for No.10 size ANC was same as No.10 size UNC, albeit there are ways of identifying whether ANC or UNC at this very small No.10 size that to all practical purposes has the same thread form/size - just variations in the tolerances. Then about the same time, but unfortunately not coinciding the relevant British Standard also changed its coding used to indicate the grade of steel - so what was a D grade for 45/55 ton mild steel was now identified as R grade. But depending on the manufacturer/supplier of the setscrews you could potentially have an ANC setscrew identified as D grade or as R grade and then you could have a new UNC setscrew still identified as D great or also the new R grade, so for XK120/140/150 potentially four British Standard variations, noting that once you got into 1960s the preferred grade of steel for these No.10 UNC fasteners was S grade, a slightly stronger 50/60 ton steel.
So in a Jaguar situation you will see FOUR main/different fasteners used for securing the Otter Switch to the inlet manifold, noting all four are HEXAGON Headed No.10 ANC or No.10 UNC - anyone who finds a round headed, slotted head screw instead has a non-original replacementā¦ NO DEBATE on that aspect 
First up you will see setscrews supplied by manufacturer BEES who supplied the first type No.10 ANC screws with BEES (their brand) and 45 D 55 branding on the head - exactly as per Dickās photos. These are identified as being ANC as apart from the added raised branding the head of the setscrew is FLAT.
When these were replaced by No.10 UNF setscrews, sometime after 1952 after running out No.10 ANC stock, we find setscrews without any brand shown, but are identified as being UNC by having a depressed disc pressed into the otherwise flat head, and for this manufacturer a simple letter R added to denote the 45/55 ton mild steel grade.
Bear in mind from the 1960s you will now find these setscrews with the letter S now denoting the later used 50/60 ton steel, but again being a 1960s introduction, should not be seen in an XK.
Now there are other variations found less commonly of these setscrews, but more from late 1950s/60s, but also note you can depending on age of XK find a mix of outgoing BEES 45D55 No.10 ANC and superseding unbranded R grade No.10 UNC setscrews. But note, regardless, these are Cadmium Plated C.7134/1 Setscrews, and not unplated nor painted CS.119/4D setscrews, noting original cadmium plating is a sacrificial coating that does wear off over time and engine bay exposure appearing to be natural steel.
Fortunately the C.723/A Shakeproof Washer used on these three setscrews is straight forward!
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Chris,
My apologies for believing Viart was correct! Iāll never do that again and first check myself.
Apparently Viart was too quick: he measured the correct diameter but the thread was absolutely wrong with 2BA at about 31 TPI and UNC at 24 TPI.
Bob K.
Didnāt realise I was starting a major discussion - ha, ha! Thanks, guys, and especially Roger for such an interesting and comprehensive post! Itās good to know that the correct thread size is ANC 3/16" 24TPI x 1/2".
I decided to remove the Otter switch from my original water elbow which was held on by 3 nasty Phillips setscrews. They were absolutely stuck fast, but careful use of the blowlamp followed by dunking in cold water eventually persuaded them out using pliers on the screw heads. One head broke off, but luckily enough of the shank was left to grip with pliers once the Otter switch was removed. The switch was junk, and anyway, I donāt use one, preferring instead to fit a blanking plate and use a manual on/off choke switch.
There will probably be a sharp intake of breath by the purists, but Iām afraid to say that although I consider myself somewhat of a purist, my affliction does not extend to correct markings on fasteners! Iāll often use stainless steel in the interests of no corrosion and being able to easily undo things in the future.
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Moss Motors sells a decent reproduction of one version of this setscrew. The version with the raised R in the center.
This link describes the varieties of setscrew heads used over the years: Otter Switch Bolts.
Below is photo from my XK150.
Regards,
Clive.
I checked your link as wellā¦
Please note - LINREAD - is as I said āother variations found less commonly of these setscrews, but more from late 1950s/60sā - as per your ālate 1950s XK150ā
The reason I emphasised the impact of the British Standards is two fold relevant in this discussionā¦
- On the introduction of the UNF/UNC British Standard in 1952 there was a requirement for all UNF bolts/setscrews to have a depressed disc into the top of the head - this was to clearly identify fastener as being UNF/UNC regardless of any other markings/brandings relative to the superseded ANF/ANC fasteners and the ongoing BSF/BSW fasteners that retained a FLAT top of head. So in any concours, if I was judging, I would deduct any Otter Switch setscrew that was not a Hexagon Head, and did not have a depressed disc in it.
- AS also noted, the British Standards denoted mild-steel grade 45/55 ton with the code letter D from post-war, up until 1952, and then the coding was changed to R from 1952/3 onwards. There was no requirement for bolts/screws less than 1/4" diameter to show the steel grading as the overwhelming majority of fasteners less than 1/4in diameter did not have hexagon heads, more usually round, cheese or other slotted screwdriver heads. But when a manufacturer made a 3/16"UNC setscrew with a hexagon head apart from the required depressed disc, they also added the letter R denoting the grade. There was no requirement to show your brand at all, and given the side of the hexagon head now with both a depressed disc and the letter R taking up most of the space, invariably there was no branding - but as per your XK150 new manufacturer/supplied LINREAD chose to add their branding.
This question was raised in context of XK140 I think - but to complete the commentary, from the early 1960s it was recommended that such setscrew applications were now made from a slightly stronger 50/60 ton mild steel; and the code used was now S, so these same setscrews seen in a 1960s Mark 2/E-type show the letter S, rather than the 1950s R.
So when I judge at Concourse if I saw an XK150 with Hexagon headed screws with depressed disc and the letter R I would be happy, regardless of any branding or not. But if I saw a round head/cheese head slotted screw, a flat topped hexagon, or a screw with the letter S (or D) I would deduct accordinglyā¦ Bear in mind, I judge in Australian Concourse where such deductions can be made - I have no view/nor comments on what prevailing policy rules are in USA, Canadian, UK nor European Concours eventsā¦
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So what happens if you have a hex head with letter R but no depressed disc?
Is it ok since itās a Nov '51 car?
As mentioned earlier, the change from ANF/C to UNF/C was required by British Standard introduced in 1952 to have a depressed DISC in top of hexagon, thus your pictured setscrews will be ANC thread (or could be BSW thread but for this application we know its ANC)
The change in a 45/55 ton mild steel being indicated by letter D, to later being now represented by the letter R happened approximately same time, but did not specifically align, so depending on bolt/setscrew manufacturer they may align, or they may pre or post align, so in this early 1950s period you can have ANC(flat)-D, albeit these are usually BEES brand, with BEES 45D55 on the flat head as per Dicks earlier photo, but you do rarely find ANC (flat - no branding)-D, ANC(flat)-R (another manufacturer who doesnāt show brand and just the R), UNC(disc)-D(potentially, but so far not yet seen) and UNC(disc)-R (usual in XK140), thus your pictured setscrews on your November 1951 are ANC-R. I would normally expect in Nov 1951 to still have ANC-D, but still have no problems with being a very early supply ANC-R, but note with stock levels/old stock you can get an overlap and indeed a mix in the one original car - and see following pic of a January 1955 XK140 - still using same ANC-Rā¦ (so old stock still??, given this is an exceptionally original/untouched car)
But for XK140 the UNC (depressed disc, no brand)-R is more commonly seenā¦
