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Part 32: Worm

 
32Worm 1902-222N°7
Pre-war double-tapped worm, remaining unchanged until the end
Loading picture worm

The parts

A very common part, used to step down gear ratios by a large amount.  The Meccano worm cannot be driven backwards (i.e. the worm has to be driven, not the gear it is meshed with).  For this reason it is useful to incorporate a worm in any mechanism that you do not want to run freely when the drive is removed, such as a crane hoist.

Round, Flat, and Chamfered ends on single-tapped worms, in chronology
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Please do not download or copy it for any purpose. It has been
kindly provided for use on this site by the image owner,
John Nuttall
Loading picture wormblanks

Chronological variations

Single-tapped worms come in three main variations, based on their overall shape without the threads.  This can be seen clearly in the photograph, in which the 'blanks' for the worms are outlined.  Early single-tapped and unstamped worms have a rounded top as per the left-hand example (and there is also a longer 15/16'' version of this with eight threads).

Subsequent examples have a 'flat' top like the middle example, and later worms have a 30° chamfer top and bottom, from the outside diameter back to 3/8'' (the boss diameter).  Examples of these (as seen on the right) are generally stamped Meccano Fabrique en Angleterre.

Early tapped worm with 6BA screw, collar with 5BA, and collar with standard 5/32 set screw
Loading picture Threads6ba5ba532 The very first tapped worms, in 1912, had a much smaller special set screw of 6BA, as shown in the photo to the right. This is an odd thread, and it has been suggested that it was the initial experiment with tapping. The special set screw is very short, and has to be tightened to its fullest extent to grip the axle. A little more force, and the head comes clean off – worms can be found like this! Perhaps for that reason, the collar (introduced a few months later in 1912) initially had a 5BA thread. We haven't found any worms with a 5BA thread, but I suppose it's possible some were made like this? It was soon realised that it was indeed possible to tap the bosses with the standard 5/32W thread, and this became the standard by the end of 1912.

Variations and oddities

Examples of six-thread worms (slightly shorter) are found single-tapped.  One is stamped MFEA so we can date it to the twenties.  Whether these are a mistake or a deliberate variation is unknown.

Early tongue-keyed worms with normal and squared thread
This image does not belong to the webmasters and is copyright.
Please do not download or copy it for any purpose. It has been
kindly provided for use on this site by the image owner,
Clive Weston
Loading picture wormsmme The photo to the right shows a selection of early Meccano worms with tongue keys (1907-1911), and you can clearly see that the right-hand two have very squared-off threads, unlike any other worms. Clive Weston notes that this part is very similar to a full-size "Acme" thread used for lathe lead screws and vices. It could well have been bought in like this and cut to length.

50s dealer packet of three worms
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Please do not download or copy it for any purpose. It has been
kindly provided for use on this site by the image owner,
William Irwin
Loading picture Wormspareparts

Dealer spare parts boxes

A picture of the top of a box of worms, probably dating from the late 50's or early 60's.  In around 1954 the Meccano internal code numbers (here 12144) started to be added to the labels.  As this is a brass part, we can't tell whether this is from the late medium red/green period or the light red/green period.

Individual part numbers

Part numbers for the parts on this page are as follows:    Unique part numbers
For identification, each variation has been given a suffix to the main Meccano part number. These suffixes consist of a two-character code for the colour, and if there are many variations, a further number and sometimes letter code to identify each variation. See the bottom of the 'Parts' page for further details.

You don't need to worry what the codes are, just click on any one for a photograph.

The button above turns on and off the display of DMS numbers (where they are known). The DMS (Development of the Meccano System, Hauton and Hindemarsh) published in 1972 and added to in 75 and 82, suggested part numbers for every variation of every Meccano part. These numbers aren't perfect, but they are recognised and also referenced in the EMP (Encyclopedia of Meccano Parts, Don Blakeborough).

More about bosses More about stampings More about paint colours
Descriptionfrom32
½'' long, feather key 02.mm
5/8'' long, tongue key 08.mm1
Square profile threads, tongue key ??.mm1a
Boss and 6BA set screw, seven threads 11.mm2
Boss and standard set screw, round end, seven threads 11.br1
Boss and standard set screw, round end, eight threads ??.br1a
Cast lead alloy, wartime 'economy' version † 16.xx
Cast iron, wartime 'economy' version † 16.xx1
Solid brass, seven threads, flattened end 18.br2
Solid brass, seven threads, flattened end chamfered ??.br2a
Solid brass, six threads, flattened end † 20s.br4
Solid brass, seven threads, double-tapped 28.br
Cast mazac, double-tapped † 41?.xx2
Blackened steel, 'Korean' part † 51-52.bs
Brass, three threads 'short' version † 51.br3
ALL

Please send us pictures of missing parts! Hints and tips for pictures
Take a picture of the part in very good light, preferably on a plain yellow background, without a flash but with a tripod.
Ideally, trim the picture to about 150 pixels per inch of the Meccano part (unless the part is particularly big or small), save it as a reasonably good quality jpg file with a filename of exactly the part number, for example 19b.ni1.jpg, and email it to us by clicking on 'Contact us' at the top of the page. Thanks!

Further information

Maxwell Roy Crago      (at 1:58am, Sat 26th Nov, 16)

I have a worm with the word MECCANO on the end of the boss, not around the circumference of the boss.
Is it rare.


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