Evening all. I can't get my head around these unf sizes. For example the 3/4 nyloc nuts that hold the front subframe bolts in, require a 1 1/6th af spanner. So do you order 3/4 or 1 1/16? The reason for my query is I want to order some nyloc nuts of different sizes and bolts to have in stock for my rebuild. I don't want to pay through the nose on eBay and thought I'd go straight to a stockist. Any suggestions on the most common sizes? Any help welcome lads

 

They are always specified by the diameter over the threads. Usual spec is diameter, then number of threads per inch. You can get different ranges of nuts in different sizes for the same thread. For example a heavy hex nut will be bigger than a standard nut for a given thread size. The 1 1/16" you mentioned is the AF (across flats) size, with has only a passing resemblance to the thread size.

I can't recall all the sizes you'd need for a front end rebuild, your best bet might to take all your old nuts and bolts into a industrial fastener supplier and match them up.

Be aware of the grade of the bolt too, that is the strength of the steel. There are many grades, but the most common are 5 and 8. On the bolt head there will be radial hash marks and it is always grade -2. For example, a grade 5 bolt will have 3 marks, grade 8 will have 6. Larger number is stronger. I would go for grade 5 as a minimum, grade 8 preferred. In Canada the fine threads only come in grade 8, not sure what the supply situation is in the UK.

Don't use stainless, those are typically the weakest bolts available.

Also be aware that for bolts longer than about 2", length is measured under the head, i.e. only the shank length, and for shorter bolts it's the overall length. I forget what the transition length is, but it's around 2". Might be 1.5".

Edit: Jaguar bolts often don't follow the hash mark convention for strength. Sometimes you'll see a number that is the tensile strength of the steel in KSI - thousands of psi. And sometimes nothing.

 

Brinny
The 3/4 refers to the diameter of the threaded part. In the UK all UNF bolts sizes of a given diameter with have the same thread pitch. The spanner size (eh 13/16th AF - across the flats) that fits the hex is not specified. I got a great assortment from Wrights Auto Supplies which did all my rebuild.
WrightsAutoSupplies.co.uk :: Bargain Automotive Fixings and Fittings UK Home or Workshop Delivery Stainless Steel Nuts Bolts Assorted Packs UNF UNC BSF BSC Metric Imperial Nyloc Stainless Braided Hoses
Decent blokes and loads of other stuff you might need.
Greg

 

It applies everywhere! UNF is a standard, means Unified National - Fine. There is also the corresponding UNC for coarse threads

As a rule for older Jaguars, UNF threads are used for everything that goes into steel, UNC threads into aluminium. Studs for the cam covers on the XK engine for example are UNC because the head is alloy.

 

Thanks very much to you both. Wrights look like a good supplier Greg thanks. Wondered why unf and unc were used now I know. Much obliged jagboi. Any suggestions on what to order?

 

Brinny
To the naked eye, UNC and metric threads can look quite similar. In the engine, into the aluminium castings (eg head, block) SOME threads are UNC and SOME are metric. This applies all over the engine, cam covers, water rails, water pump studs etc etc. There is no consistency and jaguar gradually changed threads over the life of the engine. If you replace a bolt with a new one, what I do is to test the old one with a UNC and a metric nut, to see which fits and so to be sure which thread you are dealing with.
Greg

 

Indeed, JB, but in the UK unlike the USA, suppliers do not generally quote the thread pitch, just the diameter.

 

The suppliers I'm used to have lots of bins and I help myself to what I need.They are separated out by fine and coarse thread sections, and then the speciality heads and metric.

 

I'm far from expert in sizing. In USA stuff, I'm guided by a couple f things. 24 in 1 is "fine", f, thread. 20 in 1 is c, "coarse' thread.


In my bit boxes I have a rough guage. compare to for defining the above. to see


When, I buy new, I take a sample. Nut or bolt.


Our local Ace franchise has an impressive collection of fasteners. I usually find what I need. Incl a CCW threaded nut fore my derelict buggy front spindle!!!


I try not to over grade. use an 8 when a 5 or even less will do. And, I try to think, sheer or tension. 8's are tough but more brittle than 5's etc. Not always best to over grade. for that reason alone.


Metric tosses me.


Carl

 

Good idea Greg thanks

 

As you have a 91 check the threads on the engine, my 6.0L is ALL metric, all studs in the heads are M8 x 1.25 not 5/16 UNC.

The 1989 and back will almost certainly be UNF/C. Although I have come across some metric on my 89.

I keep a couple of test nuts to check threads before replacing anything. UNF is pretty obvious but UNC can and does look the same as metric.

 

My 1985 engine is a mixture of metric and UNC, Warren.
Greg