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US Meccano Bolts

 
 
Meccano Bolt

Meccano generally used nuts and bolts with 5/32 BSW threads (5/32" diameter or 0.156" or 3.97 mm, with a British Standard Whitworth thread form). It has been discovered that US Meccano used #7-32 thread, which is a few thousandths of an inch smaller than the 5/32 BSW. This picture shows British 5/32 BSW bolts nearest the scale, and US #7-32 bolts to the right. The nuts across the top are a 5/32 BSW at the left, and a #7-32 at the right. The nut in the middle is probably a #7-32 nut, but some 5/32 BSW bolts will fit. It is apparent that these nuts and bolts are very difficult to distinguish.

For comparison, dimensions of these threads, along with more commonly available (at least in the US) #6-32 and #8-32 sizes, are shown here (dimensions in inches and, in parentheses, millimeters):

Outside Diameter (max) Pitch Pitch Diameter (max)
#8-32 0.1640 (4.166 mm) 32 tpi (0.794 mm) 0.1473 (3.741 mm)
5/32 BSW 0.1563 (3.970 mm) 32 tpi (0.794 mm) 0.1362 (3.459 mm)
#7-32 0.151 (3.835 mm) 32 tpi (0.794 mm) 0.1307 (3.320 mm)
#6-32 0.1380 (3.505 mm) 32 tpi (0.794 mm) 0.1177 (2.990 mm)
(tpi = threads per inch)

The full story is rather long and detailed - it is available as a .PDF (Adobe Acrobat) file by clicking on the picture or here. Warning! This file is large (417 KB), and will take some time to download (I have found around three minutes on my dial-up modem). You might find it easier to right click and "Save Target As" or similar command to save the file directly to your hard drive.

This file has been revised on 14 November 2003 - while I was in Toronto at the Hobby Show (and the CMAMAS meeting), Don Morton was kind enough to point out some errors at the bottom of page 9. The last two lines should read "...average value. e is the constant 2.718281828459045. For this example, A and B are 1; C is 0."

 
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