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Part 32: Worm

32	Worm	1902	-	2	2	2	N°7

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.

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.

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.

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.

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).

Description	from	32
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!

• A greyed-out box shows that no part exists for that colour combination.
• Part number codes with a green background have an attached picture of the part, just click once on the code to show a photograph of that part in a separate window.
• Parts marked "†" were temporary or economy parts, or existed only within specific themed outfits. The previous part continued throughout or afterwards.

Further information

Total number of messages on this page: 10.  This is page 1 of 2.   

Mman      (at 6:25pm, Sat 2nd Jan, 21)

I have discovered that the cast lead worms are smaller in diameter than the brass ones. Also there are two different pitches of worm, only a slight variation noticeable if you try meshing two together.

Mman      (at 6:22pm, Sat 2nd Jan, 21)

You can normally tell the difference just by glancing - left hand threads just look wrong. Look at the worm held vertically, each thread ridge will slope down from right to left for a right hand thread and slope down from left to right if it is a left hand one.

John Shervington      (at 4:44am, Mon 19th Oct, 20)

How do I tell the difference between the right-hand standard worm and a left-hand standard worm.

itawah      (at 2:45pm, Mon 11th Nov, 19)

Ciao a tutti vengo dall'italia / itawero

itawah      (at 12:11am, Thu 7th Nov, 19)

Ciao a tutti vengo dall'italia

checkvilWet      (at 2:31am, Wed 21st Aug, 19)

i am Checkvil. This i my login on this forum. it is good ? :)

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