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Parts 95-96a: Sprocket wheels

95	Sprocket wheel, 2''	1915	-	3	3	2	N°8	36 teeth
95a	Sprocket wheel, 1½''	1922	-	4	4	2	N°10	28 teeth
95b	Sprocket wheel, 3''	1921	-	2	2	2	N°9	56 teeth
96	Sprocket wheel, 1''	1915	-	10	10	4	N°8	18 teeth
96a	Sprocket wheel, ¾''	1922	-	3	5	2	N°8	14 teeth

The parts

The picture above shows all five sizes of sprocket wheels in the Meccano system.  Matt black sprocket wheels are post-war, and the most common colour scheme.  There is one more often overlooked (see, I nearly did it there), which is part 168b the toothed disc section of the ball thrust bearing.

In combinations, these sprocket wheels can create a number of very interesting gear ratios.  More than that, it's also not universally known that the standard Meccano spur gears are designed to work with the sprocket chain over every alternate tooth.  This gives us wheels with 25, 28½, 30, 47½, and 67½ effective sprocket teeth to go with the 14, 18, 28, 36, and 56 shown above and the 73 teeth of the toothed ball race.  Truly a huge range of ratios available!

Interestingly, 73 is a factor of 365, which can come in handy building simple orreries or complex clocks.  It would be interesting to know whether Meccano planned this fact deliberately.

Chronological variations

Tooth shape

The most significant change in the sprocket wheels is in the shape of the earliest teeth.  These are normally described as "rounded" or "semicircular".  Without photographs this is about as accurate as we can get.  However, I believe that there are three shapes – semicircular, then slightly rounded, then the final pointed shape that became standard on all versions after the nickel-plated ones.

The photo above right shows the three different types of teeth, which can be seen (I believe) only on the 1'' and 2'' sprockets.  This would date the change to pointed teeth before 1921/2, when the other sizes of wheels came into the system.  We would need to find a dated and unused inventor's outfit to improve on this date.  Or, we can move it on if we find other sprocket sizes with the slightly rounded teeth.

Large bosses

There is a strange sequence of bosses in the largest (2'' and 3'') sprocket wheels during the 20's.  The easily overlooked part of this is that the large (half-inch) boss is seen in two types.  The first is an enlarged copy of the smaller boss, but the later version is of an improved design where the central hole is not circular.  This prevents the boss from slipping in the part, an important consideration in the larger sprocket wheels.  Compare this with part 19b (the 3'' pulley), where the large boss was simply dropped from the part.  Clive Weston speculates on the sequence of events:

I have fiddled with the dates above, but this hypothetical sequence does match up with other parts found.  The 3'' pulley part 19b changes to a half-inch boss at the introduction of the 3'' sprocket, and loses it at a similar time (just after dark red paint comes in).  It didn't regain it, probably because there is nothing like as much torque on a 3'' pulley.  Part 27b (the 3½'' spur gear), starts with a single-tapped large round boss (in 1924), but changes directly to the improved half-inch boss at the same time as the 95 and 95b adopt them.  This part breaks the above sequence as it is not known with a small boss.  However, it does change from the old to new-type half-inch boss at around the same time.

There is a little more time available for this change than is usually thought.  Sprocket wheels didn't appear in dark green until much later than ordinary Meccano parts, lasting well into 1928.  In a mint December 1927 outfit the 2'' sprocket is still nickel, and has the small double-tapped boss.

The following entries in the Meccano Magazine and other manuals show the sequence of sprocket wheels appearing around these dates.  Note that the date of publication shows only that the part existed a short time before the printing date.  It could have existed perhaps 6 to 12 months earlier than this in some instances.

• 2" sprocket with 8 holes and small boss
• First example in June 1924 MM, page 151, in Single Cylinder Steam Engine, later to become SML11 (all previous versions have no holes).
• Small boss and 8 holes also clearly visible in April 1925 MM p166/7 (Bagatelle table), July 1926 MM p435 (Standard Mechanism 106), Jan 1925 MM p45 (Suggestions Section), July 1928 MM p603 (nonsense model).
• 2" sprocket with 8 holes and later-type large boss
• First appearance with ½'' boss is in 1929 Standard Mechanisms manual (529/40), printed May 1929.
• Also shown in SM166, p31 (Traction Engine steering) and in SM202 (gantry crane trolley).
• The entire gantry crane referenced is shown in July 1929 MM, p557.
• SML21 Transporter Bridge (printed November 1928) shows in the main picture what looks like the large flattened peening but in Fig.3 it appears to be a large early boss.  The peened side is slightly out of line with the boss suggesting faulty retouching, so this is perhaps inconclusive.
• 3" sprocket with early half-inch boss
• The introductory picture in Nov/Dec 1921 MM mistakenly shows a 1'' sprocket, so we can't see the original form.
• First known picture in Nov 1925 MM p560 in Standard Mechanism SM7, also in SM manual from late 1925.
• Also shown with half-inch boss in No.7 manual models Aeroscope and Funicular Railway.
• Pictured in the 1926 and 1927 colour leaflets with half-inch boss.
• 3" sprocket with small boss
• Supermodel 4 (Block-setting crane) and 33/33a (Single/Double flyboats) both show the 3'' sprocket wheel clearly with a small boss.  The first printing of these is June 1928 (SML4) and April 1929 (SML33).

Note that in the 1927 and 1928 manuals (last printing May 1928) the sprocket wheels are marked with an asterisk and noted as being only available in nickel finish, as described above.  Green sprockets date therefore from some time after May 1928 and before March 1929 (when the asterisk is missing).

What assumptions can we reach from this? Well, to start with, there should be no such thing as a 2'' sprocket with a half-inch boss single-tapped.  There should be no 3'' sprockets with small single-tapped bosses.  And there could perhaps be a 3½'' spur gear part 27b with a small double-tapped boss, but one has not been found (perhaps for the reasons given above).

We can speculate that the 3'' and 6'' pulleys (parts 19b and 19c) were not given the new version of the half-inch boss because they are made from two thin pieces of steel, rather than 95, 95b, and 27b that are made from significantly thicker stock.  Perhaps some part of the process made using these flattened bosses more difficult to add to the other parts.

Black variations

After nickel plating, the sprocket wheels went through a range of colours along with the pulleys and many other parts during the 30's, then settled on black when they were reintroduced after the war.  But there is more than one black, as I hope to show from the picture to the left.  It's extremely hard to get photos of these blacks, but we can try.

Top right is the common post-war matt black, which you will notice is very subtly textured.  Top right is what I have called "blue/black".  It's noticeably different, and you don't need to have it next to a black one to spot the difference in reasonable light.  The finish is smoother and less matt than the earlier one.

Bottom left is the gloss black version – these are a full gloss and easily identifiable.  Martin Hanson has confirmed the existence of these two types.  It is thought that the blue/black coincides more or less with the start of the silver/yellow/black period in 1964, and the gloss black from the start of blue/yellow/zinc in 1970.

At the very end of Binns Road production, sprockets changed to dark yellow.  When reintroduced, they were finished in a heavy gloss blue/black paint as you can see from the example bottom right.  The colour is similar to the UK production (although obviously they aren't stamped Made in England), but the thickness of the finish is also easily spotted.

Variations and oddities

None known

Dealer spare parts boxes

I have a bunch of pictures of post-war boxes which I'm sorting out now...  if anyone has any not in the yellow boxes that would be interesting...

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	95	95a	95b	96	96a
Nickel, 1/16'' face, semicircular teeth	??	?			.ni5
Nickel, rounded teeth, no holes, single tapped boss	??	.ni4			.ni4
Nickel, rounded teeth, no holes, brass single tapped boss	??	.ni4a			.ni4a
Nickel, rounded teeth, thin steel, brass single tapped boss	??	.ni4b			.ni4b
Nickel, rounded teeth, thin steel face with no holes	??	.ni4c
Nickel, pointed teeth, no holes, single tapped	??	.ni2			.ni	.ni
Nickel, pointed teeth, no holes, double tapped	??	.ni2a?			.ni1	.ni1
Nickel, with half-inch diameter boss single tapped	21?			.ni3
Nickel, pointed teeth with all holes, single tapped	??	.ni	.ni
Nickel, pointed teeth with all holes, double tapped	27?	.ni1	.ni1	.ni1
Nickel, with new half-inch diameter boss double tapped	28?	.ni3a		.ni3a
Dark green, double tapped	28	.dg	.dg	.dg	.dg	.dg
Royal blue	34	.nb	.nb	.nb	.nb	.nb
Royal blue with blue painted boss	34	.nb1	.nb1	.nb1	.nb1	.nb1
Medium red	37	.mr	.mr	.mr	.mr	.mr
Matt olive green, only two holes, (Mechanised Army) †	39-41		.ma		.ma
Matt black	47	.bk	.bk	.bk	.bk	.bk
Blue/black	64?	.bk1	.bk1	.bk1	.bk1	.bk1
Gloss black	70?	.bk2	.bk2	.bk2	.bk2	.bk2
Dark yellow	79	.dy	.dy	.dy	.dy	.dy
Dark yellow with yellow painted boss ³	79	.dy1
Gloss blue/black	85	.bk3	.bk3	.bk3	.bk3	.bk3
		ALL	ALL	ALL	ALL	ALL

Note: There are many other variations on the above nickel plated parts shown in DMS/EMP, but for the moment I've left them off pending photographs of all the variations shown.  Whereas there are documented variations like "no holes", "two holes", and so on, it's not always clear about the tooth shape, tapping, or whether the boss is nickelled or not.  Hopefully we will be able to find most documented variations and no doubt some more too, which will be added to the table as and when they are found.  Those parts that are suspected to exist are marked with a question mark above.  The proposed numbering scheme is: .ni = 'ordinary' single-tapped parts, .ni1 = as .ni but double-tapped, .ni2x = "variant" single-tapped parts, .ni3 = half-inch bossed parts, .ni4 = rounded teeth parts, .ni5 = semicircular teeth parts.
All nickel-plated sprocket wheels have nickel-plated bosses unless identified as brass above.
²  The only two-hole sprocket part 95 found so far looks very much like the holes were drilled at a later date, as noted in "variations" above.  Until we find another example of this, it's not likely that this is a genuine part.
³  This appears to be a black sprocket overpainted dark yellow, using up the old stock of parts. There's no reason why other sprocket sizes might not turn up painted this way.

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: 11.  This is page 1 of 2.   

Michael Hewitt      (at 3:21am, Thu 26th Jan, 23)

I have at least one 96 from each of the post-war, SYB and BYZ eras with the plate mounted upside-down (stampings toward the body of the boss).

Fernando      (at 2:40pm, Thu 9th Dec, 21)

Sorry, it was an involuntary mistake not to put my name, I tried your suggestion Michael it works perfect, thank you very much, Fernando from Chile

Michael Walker      (at 2:00pm, Thu 9th Dec, 21)

In reply to "Anonymous" below, I would suggest leaving the chain link in, but taking up the slack with an extra 'jockey' sprocket wheel, as shown on page 74 of the February 1970 Meccano Magazine. This may be accessed via the "Magazine" tab near the top of this page.

Anonymous      (at 12:59pm, Thu 9th Dec, 21)

Hello friends of meccano, I have a query, sometimes the chain that is installed on two sprockets to produce movement, when it moves it has small jumps in the toothed part and I have tried to shorten the chain, but when it is very tight, it does not works fine, any suggestions?

bob t      (at 9:39am, Sat 10th Jul, 21)

KJAY, use a screwdriver to prise open the ends, then add or remove links as necessary. I personally would use long narrow pointed pliers to open the ends of the wire links. Then close gap to finish off.

KJAY      (at 12:37am, Sat 10th Jul, 21)

How do you break a meccano chain then rejoin to required size

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