Knurled Brass Spark Plug Nuts and Veteran Spark Plugs and Accessories - Various Types

Product no.: 0895 HT_Nut01

In stock

from £2.20
Recommended Retail Price, plus delivery

This listing shows a selection of brass fittings for veteran motorcycle spark plugs, as well as some rarer spark plugs and fittings (and a nice copy of the Veteran Lodge style brass cooling fins that fit over most spark plug types).  We have manufactured the knurled brass nuts for securing the HT lead on older motorcycles (i.e. pre spark plug cap) in two main styles and a variety of threads.

Note: see also Item Listing 0896 - since originally starting this multi-item listing, I have now listed our 18mm KLG type spark plugs seperately, along with 18mm/14mm copper abestos type spark plug sealing washers.


Spark Plug HT Lead Nipple/Knurled Nut Background:

If you have an older historic motorcycle - i.e. pre WWII or earlier, then you may decide you wish to fit the HT lead to your spark plug with a brass connector, rather than with a more modern HT Spark Plug Cap (of which we also sell in various styles).

Like many old motorcycle enthusiasts, over the years of collecting I have accumulated a selection of old spark plugs of various styles, and some of these go back to the earliest motoring days of the 19'teens - 1920's.  When recently I was looking to fit spark plugs to my own 1919 Douglas 2 3/4hp project bike (used for some of the photos in this listing), I decided to fit period 18mm spark plugs and our ochre coloured cloth/waterproof HT lead, along with veteran style brass HT clip connectors (i.e. pre plug cap) - which would have been correct for a veteran bike.

To go with this I investigated the different style of knurled screw on nuts which were commonly fitted to these early type of plugs, which allow the brass HT connectors to be easily screwed on our taken off.  I was suprised to find there were lots of styles and variations over those early days - but by far the most common type was the knurled adjuster with a design commonly seen fitted to Champion spark plugs.

However, I also have an example of a very pretty Lodge type of knurled nut - which has a wider top knurl diameter and a concave tope.  As well as giving good purchase when tightening the HT lead to the plug - I think this type of knurled is very pretty, and quite rare now.n

Therefore - we have replicated  both these definitive styles - the bigger diameter Lodge type being an almost identical copy of the original nut, while the other small type is copied from an original definitive type used on a 1920's Champion plug (note - I found numerous nuts of this style, many with minor variations over the years - but chose an early type of the most definitive design).

Both knurled nut types are CNC machined in brass by us and can be supplied in a variety of threads - the sub listing items representing the most commonly used spark plug top threads used.  


Early Spark Plug Brass Cooling Fin - based on Lodge original, to fit most spark plug types (0895_8):

As you can see in the first photo, in my spark plug collection I have an unusual and very pretty/rare pink Lodge H1S spark plug (New Old Stock), which has the addition of a brass cooling cap with fins, which sits atop the porcelain.  I have seen similar brass cooling fins fitted to the very earliest (i.e. Edwardian) motorcycles and cars and they give a lovely period look to an older motor vehichle restoration.

We have reproduced this finned cooling ring - to an almost identical profile, but underneath, the ring counterbored so that it will fit on top the porcelain of almost any spark plug - including modern plugs.  By so doing, if you wish, you can use modern spark plugs (with make scrubbed off if required!) and this ring placed on top of the porcelain to give the plug a much older and pretty look. 

We offer this cooling ring, along with the knurled 'Lodge' type HT nut (specify which thread type for nut when ordering)  - as shown in the photos associated with this item - including them having been fitted to the KLG 18mm ML50 plugs we also offer here, fitted to my own Douglas 2 3/4hp project.  I have to say, they nicely finish off this area of the restoration.

Spark Plug Top Thread Background:

Until we came to make these knurled HT nuts, I had always assumed the top thread used to hold the HT nipples on spark plugs was a standard thread - standardised on all spark pluge going back to the earliest days - No such luck!

It turns out there were numerous threads used over the years - and I do not think we have found them all!, however I think we have identified the 4 main types (and two seem most commonly used), and have made the two knurled nut styles in sub-types to take into account the different thread types.

I have also gone through my own spark plug colletion and tried to identify the different Makes and Styles that used the different thread types - I cannot be sure that if you have the same spark plug in your collection, it will have the same thread (as they may have changed by year) - but in the accompanying photographs, I have showed some of the plugs with their various thread type in the sub listing to help you select which one is right for your plug.

If not sure - I would suggest you buy one of each (!) . . . but do not try and force on by more than two threads or the brass may strip.  

I cannot be sure this is definitive - but in general I found the following threads used on the following plugs (see photographs that accompany the individual items):

- 8 UNC Thread (0895_1 and 0895_4):  

  - Champion:  I found a number of the older (or US branded?) Champion plugs fitted with this metric 8 UNC Thread.  Those tried with this thread included: Champion N5 (common 14mm 1960's - 1980's plug/ C5 (22mm plug) - both early 1930's rounded ceramic type and later (1960s style multi ridged type) / J10-COM/ L7 (another 14mm 1960s style plug)/ D8C - this last plug is a rare 18mm long reach plug with an unusual extended 3 prong electrode - they are a possible alternative for Douglas 2 3/4hp engines - but you need to ensure electrodes will not fould valves.  I have a pair of 'New old stock' D8 plugs as the on-bike spares. 

  I suspect as Champion was commonly sold in US, that earlier Champion pluges were predominantly this thread - but not entirely, see below in metric threads.

  - KLG:  FE75 14mm plug (1950s style plug?) 

  - Lodge:  Some Lodge threads were UNC, others were metric.  Three of the pink ceramic Lodge plugs I have in my collection were this 8 UNC thread - CANY plug (common 14mm plug), HL14S (pink ceramic 14mm plug - but with earlier seperate hex component for locking in cermaic and H14S with brass cooling fins fitted (this last plug was the one with the big knurled Lodge nut and cooling fins shown in many of the photographs - that we used as a template for 0895_5)

  - Wipac Pacey: F2.0 - blue ceramic 22mm plug

  - AC :  AC 78 22mm plug, made in the USA.  Note, in the accompanying photograph there is a second very similar plug to this, which is also 8 UNC - but has no marking whatsover.  I think this second plug may be another AC or possibly a Bosche make

  - Autolite: In the accmpanying photograph is a 'new old stock' Autolite A652.  Not a common plug - but I believe a 1960's-80's 14mm long reach plug 

- 4mm x 0.70mm Thread (0895_2 and 0895_5):  

    -  NGK: This looks to be the thread adopted by all modern NGK plugs - in case you want to fit a good quality, easily available, modern (14mm) plug  on your old motorcycle, but still use these knurled brass nuts for a period look.  NGK plugs tried included B6ES (common 14mm long reach, including fitted to many british bikes), B9HC and B77HC

  -  Item 0896_1 KLG Plug: Our 18mm KLG ML50 new plugs (Item 896_1) use this metric thread.  Note; as supplied these plugs come with the normal HT cap modern round nut - so if you want to use a knurled nut, they are with this thread

- Original KLG: KLG FE100 14mm plug, which is 'new old stock' and looks to be of 1950's-60's vintage.  Note: this plug looks very similar in appearance to the FE75 plug above, which is UNC - so it looks like KLG at this period used both thread types!

  - Champion:  I found at least one more modern Champion plug fitted with this metric 0.7mm Thread - Champion N62R (1970's-80's racing plug.  I would not be suprised to find more modern Champion plugs also fitted with this metric thread

- Lodge : This is probably the most difficult make of plug to identify thread for - as I found plugs of same 1930's - 1960's (pink ceramic) era with both metric and UNC thread type.  Those found with this 4mm x 0.7mm thread were - RL51 (the famous racing type plugs so favoured on Manx Norton's, 7R's, KTT's etc) / 2HLN / 3HLN

- 3 BA Thread (0895_3 and 0895_6):  

    -  KLG (very early?): I have read that 3 BA thread were fitted to a few spark plugs.  In my own collection I have only found one plug that uses this thread - but it is the very early KLG Brown Mica ceramic type - model number LK1 (the oldest plug in my collection).    It should be noted that a similar KLG plug to this one - the HS1 type was listed as original fitment for Douglas 2 3/4hp models (amd I would be interested in purchasing if you happen to have 2 of these in working order!)

- 4mm x 0.75mm Thread (0895_7):  

  Similar to the 3 BA thread, I have read that the 0.75mm pitch (4mm) thread was also sometimes used on spark plug HT nuts.  In my own collection I have only found one NGK plug (and an obscure one at that!) that uses this thread, but I have made a small quantity of Champion style nuts with this thread, just in case you want one!:

    -  NGK:  I have one older style NGK plug - an unusual C10M (see photo) plug which employs this less well known 0.75mm pitch thread.  It may also have been used on other early NGK or other makes of more modern plugs.  


- Other thread types not catered for:  I have one other pluge - an 18mm Lodge from the 20's-30's which has white porcelain and a larger 10 UNF fine thread.  I think  this plug is possibly from a motor car, and the top thread may be intended for a wire style HT top clip, not knurled nut.  I have not made nuts for this obscure plug - but if you know of a this or other threads (with some market!) I may consider making a small batch to htat thread (email our normal

Final point.  I am not intending to make any other brass spark plug parts in the near future, but if you believe there is a particular type missed or fitted to early Edwardian or Norton motorcycles - then let me know and we will consider making a batch.

Likewise - with older style spark plugs, we are able to supply a small quantity of the rare KLG 18mm long reach plug (similar to fitted to early Douglas motorcycles and possibly some early Norton engines) - but do not have any plans to supply others.  However, if anyone knows of good quality 18mm long reach plugs still available, we would be interested to hear, thanks 


Customers who bought this product also bought

Recommended Retail Price, plus delivery

Browse these categories as well: 1z. Douglas 2 3/4hp and 1912-25 Douglas/Edwardian Parts, 1.g Norton ES2/16H/OHV/SV Parts, 3a. BTH KD1, Lucas Magneto/MagDyno and Ignition and HT Parts, 1.q Norton 1920's and Earlier 1930's Models - All Parts/All Models