Wyn, one day I will provide a comprehensive write up of Jaguar fasteners, with the immediate post-war period, including the XK120, a particularly volatile period given the arrangements that were put in place during WW2 by the British Ministry of Supply, that progressively became enshrined in revised, and indeed totally new British Standards during the 1940s and 1950s.
The particular WASHER you are asking about, is identified in the J.8 SPC as being an FW.208/T Washer, Plain, on Bolts. and note, it is shown as being 6 off.
Now you need to appreciate, the coding FW.208/T is based on the WW2 British Ministry of Supply arrangements, adopted or extended by post-war British Industry including Jaguar Cars, and the various companies making nuts, bolts, washers etc as being a ‘Standard’ fastener. If Jaguar wanted anything else, it was a ‘non-standard’ fastener, which then required Jaguar to allocate their own part number (C-prefix for Chassis related items, and BD-prefix for body related items), and prepare their own engineering drawing detailing exactly what they wanted - it could be simply an otherwise ‘standard’ bolt, but needing a hole drilled in it for a split pin, or a ‘standard’ washer required to have a special finish such as being plated, and not the manufactures own default finish which is another important subject for XK120 fasteners.
But an FW.208/T Washer is a ‘Standard’ washer according to the British Ministry of Supply, as used by Jaguar and as recognised/used by the various British suppliers of washers, and was incorporated into relevant 1940s/50s British STandards that were revised/updated from time to time.
But immediate postwar, this FW.208/T ‘Standard’ washer part number, can be decoded as follows…
Fx. = BSF thread. (This effectively tells you that the nominal Bolt diameter is as per BSF specifications, and in the case of standard washers effectively tells you the nominal hole diameter)
xW. = a standard Washer. (that’s straight forward, but later codes tell you more about the type of Washer)
So far, all we have is the FW. prefix means a generic 'nominal BSF Washer - and no Rob it does not mean ‘Flat Washer’. The body of the code now gets specific…………
.2xx = for a Washer the 2 denotes being a heavy-duty plain washer. (a 1 denotes being an ordinary plain washer).
.x08 = the size of the washer, in this case the 08 is 1/2 inch nominal BSF bolt size with the actual hole diameter having set tolerances (the British Standard says for a 1/2" BSF washer, the actual hole diameter must be 0.515" to .520" thus I have adopted my own system of showing these nominal sizes as being in this case 1/2" Ф )
So now we know our simple ‘Washer’ as referred to in the SPC is in fact a nominal 1/2"BSF heavy-duty plain washer. Now the British Ministry of Supply, and indeed the relevant British Standards tells us more exactly what that is.
A heavy-duty 1/2"BSF (nominal D) washer is 1-1/8" Outside Diameter (dimension C), with a 0.515" - .520" Internal Diameter (dimension B) and an ‘approximate thickness’ (dimension A) of 13 S.W.G (British steel gauge that equates to 0.092")
(now it should be noted that heavy-duty washers were one Outside Diameter increment larger than their equivalent ordinary plain washer - in the 1/2"BSF size a plain washer is 1" OD, and depending on size may also be one gauge increment thinner, albeit in the 1/2" BSF size still a plain washer is still13 SWG)
Now as Godfrey has pointed out, there is a most useful table on page 99 of the SPC which indicates that all FW.208/T washers are ‘Bevelled’. This in fact is not correct, and I can quote the source from the British Standard …….
15. Plain washers…………………… They may, at the option of the manufacturer, have a chamfer of approximately 30 degrees on one face.
Note ‘at the option of the manufacturer’.
This of course explains why those who have closely studied actual XK fasteners will be aware that although there are many uses of FW.2xx series heavy duty washers, although always of one diameter increment larger (for the nominal bolt size), they are regularly found ‘bevelled’ or ‘flat’ without any bevel, so no surprises finding flat FW.208/T washers on an XK120. There are other manufacturing characteristics not specified in the British Standards, thus for those that care about pedantic detail, should seek out and restore the correct original fasteners, rather than buying new - with the new ones not necessarily to 1950s dimensions/tolerances nor indeed manufacturing characteristics.
Re the topical FW.208/T their are two residual aspects…….
The /T suffix denotes the material used, and in the case of a plain Washer /T denotes STEEL. The British Standards will specify the exact grade of Steel, being a pretty basic uncontrolled strength mild steel, somewhat inferior to the 45/55 ton /D grade steel used in bolts and setscrews. (Washers used by Jaguar can also be found in grade /X = Spring Steel, /E = Copper and /C = Brass)
The final detail is what finish is applied to the steel washer, if any.
As per my introduction above, if Jaguar had wanted these washers to have any special finish then they would no longer be a ‘standard’ fastener, but a ‘special’ fastener required/supported by a C.xxx prefix part number engineering drawing So they are NOT plated, as is say the C.793 Washer, Spacing shown Chromium plated in the photos.
For standard Washers all the 1951 issue British Standard requires is…….
" The bolts. screws, nuts shall be cleanly finished, sound and free from defects" (Washers don’t rate a specific mention)
What that means is you got whatever the manufacturers ‘default’ finish was, depending on item and how they made it. Normally in practice, things were either left bare-untreated steel, often given a basic protective ‘blackening’ process, which during the XK period was invariably one of the many proprietary hot chemical-conversion bath processes that gave a black-oxide finish, and indeed as students of XK120 BEES bolts will appreciate, sometimes a simple red-lead dip. My observation of ‘standard’ XK washers however, is those not over-painted in an assembly, were most probably black-oxided. And if Jaguar was not happy with that, then all they needed to do (but didn’t) was instead buy these in as ‘Special’ fasteners with a Cxxx part number, and nominate their required additional surface finish treatment.
So my advice to anyone wanting to restore their XK120 to the most authentic standard possible, and in a no-maintenance show condition, read the J8 SPC carefully (and don’t jump to wrong conclusions), but you cannot go past these exposed ‘standard’ fasteners having a black-oxide finish - and never plated.