Unique Marshall cab screws

[GAR]

Ugh..

I have sold some really old cabinets, now that I'm almost clear I can walk thru storage unit and get to some ones I had in project stages for people.

So I pull a baffle on one cabinet to go look for screws and I find neither American Standard ("sae" measured in threads-per-inch) nor Metric (mm per something metric) and I make the sheer discovery by accident of learning about the Whitworth screw I'd like to share.

Some of you may have come across this not knowing what it is, but in these older cabs they threaded the speaker baffles with two kinds of thread: one was a pushed-in little barrel looks like a headless rivet which I don't know the name of.. the other is the thing we all know and love, the "tee-nut."

This thing has a neck that gets pushed into a screw hole in the face of the baffle, while a spiked flange at the end of it touches into the face and bites down, gripping the plywood and preventing the threaded neck from spinning in either direction such as when you'd remove or replace a speaker.

So I am frustrated - Im digging thru all toolboxes I have looking for the baffle screws, ending up taking the thing to several hardware stores.

I don't care! I get looks, you know and don't care.. I've wheeled in cabinets, even Marshall head cases trying to find the exact match and insuring the screw actually threads before I buy it by driving it in right there in the aisle at Home Depot.

So I am getting nowhere. I had done this once in the late 80's with an old cab I was restoring and forgot how I got by that time - I think I either reinstalled new Metric tee-nuts and regrilled that cab, or got brass screws and forced them in, deforming to the weird thread with the closest metric equivalent.

Then I get to this TruValue hardware store with one of those really old guys who know everything from 60 years ago, I show him the baffle and explain it to him and he goes "gee, you've got the Whitworth there.." and pulls out a gauge, lining perfectly within the teeth like a finetooth comb stuck in bookpages.

Unfortunately, no screws to be had so I had to retap all 16 fasteners with a 5mm X 0.8 pitch thread hand tap cutter.

Pretty easy but time-consuming: some WD40 on the cutter, and you thread it down into the teenut, backing out one full turn about every three turns in to clear the cutting, and then wipe off the debris from the teeth when you back out and it's done.

I've had to do 3 baffles this way last month: I don't care that the screws are not original because the old ones cross-threaded too easily and the Metric heads are much wider holding the speaker way way better when using lockwashers.

Also, the Metric screws are easily replaced anywhere, and much cheaper than the more hard-to-find Whitworth.

If you have an older cab with funky but fuckedup speaker screws, don't go missing one. Just retap them all!

I remember once I had bought a cab missing FOUR screws.. and in trying to figure out why, it seemed there was one cross-threaded teenut somewhere at each speaker position so the guy whoever did that, just got by with holding 'em with 3 each.. if he only knew.

Cost of repair: 2 hour 45 mins first time, most recent time, 1 hour 15 min.

Tap: 5mm .8 pitch metric tap $3.99
Tap Handle: $6.99
WD40 penetrating oil: $1.79
16 Screws 5mm x 25mm: $3.20

80 year old fart tinkerer advice: priceless

[GAR]

British Standard Whitworth - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/British_Standard_Whitworth)

History

The original Whitworth thread form was proposed by Joseph Whitworth (http://en.wikipedia.org/wiki/Joseph_Whitworth) in 1841 to replace various proprietary fasteners. This standard specifies a 55° thread angle and a thread depth of 0.640327 p and a radius of 0.137329 p, where p is the pitch. The thread pitch is specified by a chart. The Whitworth thread system was later to be adopted as a British Standard to become British Standard Whitworth. Contrast this with the American Unified Coarse (http://en.wikipedia.org/wiki/Unified_Thread_Standard) another standard based on imperial fractions used in the United States. These are similar except that the Unified thread angle is 60° and has flattened crests (Whitworth crests are rounded). There is one important exception in this comparison; the thread pitch for the 1/2" bolt is 12 threads per inch (tpi) in BSW vs 13 tpi in the AUC.
With the adoption of BSW by all the British railway (http://en.wikipedia.org/wiki/Railway) lines, many of which had previously used their own standard both for threads and for bolt head and nut profiles, it came to dominate mechanised British manufacturing.
In the USA, BSW mostly died out as steel bolts replaced iron, but was still used for aluminium parts into the 1960s and 1970s when metric (http://en.wikipedia.org/wiki/ISO_metric_screw_thread) based standards replaced the Imperial ones. In some other countries, such as Australia (http://en.wikipedia.org/wiki/Australia), BSW is still heavily used.

[edit (http://en.wikipedia.org/w/index.php?title=British_Standard_Whitworth&action=edit&section=2)] Comparison of standards

The British Standard Fine (http://en.wikipedia.org/wiki/British_standard_fine_thread) (BSF) standard has the same thread angle as the BSW, but has a finer thread pitch and smaller thread depth. This is more like the modern "mechanical" screw and was used for fine machinery and for steel bolts.
The British Standard Cycle (BSC) standard which replaced the Cycle Engineers' Institute (CEI) standard was used on British bicycles and motorcycles. It uses a thread angle of 60° compared to the Whitworth 55° and very fine thread pitches.

[GAR]

Thank G-d Marshall went fully with Metric by the 1970s, or we'd have more of this problem when changing speakers out than already is out there!

I'd like to just know one more thing: when did Marshal do this?

I know how to recognize this screw by the flat face of the head and that it is a slot-screwdriver head not a Phillips. But to my recollection, I believe I have seen this screw in cabinets up to the late 70s by going just with teh speaker date codes.. though not sure at all WHEN it disappeared from use!

[Diamondjimi]

http://www.sondrak.com/archive/skpics/crickets%20chirping,jpg

[ELVIS]

That's funny...:D