[TR] How to tell the size of bolt or setscrew from the part number?

Michael Porter mdporter at dfn.com
Wed Jun 17 15:59:19 MDT 2020

On 6/17/2020 2:07 PM, Sujit Roy wrote:
> Hello Don,
> I have the standard triumph hardware catalog and have to refer to it 
> all the time. I do see some sort of sequence with the last digit, but 
> other places that sequence is off.

The system has to be designed to accommodate this, and I don't think 
either the S-T or B-L systems do.  And most manufacturers do this 
differently.  For example, GMC simply assigns part numbers 
sequentially.  An engineer needs a part number for a new a/c part and 
goes to the parts book, creates the next new sequential number and a 
description.  The next engineer comes along and needs a new suspension 
part and so the next new number, one number apart from the last one, is 
a ball joint.  Part numbers for the component parts of an assembly are 
usually assigned by the people writing the parts manuals, and that's 
where you'll often see consecutive part numbers for similar part types, 
simply because they're doing breakdowns of a purchased assembly all at 
one time.

I understand the pitfalls of this system since I wrote parts manuals for 
a GMC product for quite some time.  One digit off in ordering fifty 
screws, and you could end up with a couple of pallets of a/c evaporator 
motors (that's actually happened).  And, lazy manual writers never 
checked to see if a number had already been issued for a part used on 
more than one type or style of purchased assembly from a vendor, so the 
number of part numbers for that part simply multiplied.  These never 
showed up in the electronic parts management system used to create the 
bills of material for each vehicle, since that was composed of top-level 
parts only, so I had to create my own searchable database to purge them.

VW, for a very long time, has had a descriptive part number. IIRC, the 
first number is the vehicle type (1 for bug, 2 for bus, 3 for 
squareback/fastback, 4 for the 4lls and 412s, etc.) in which the part is 
first used, the second is a two-digit code for where on the vehicle the 
part was first used, then a code for part type, then a two or three 
digit code for size and then a sequential number indicating that it's 
the xxxx part of that configuration used in the manufacturing history.  
As VW expanded its model line and options, they appended an -xxx number 
to a part to indicate its use for trim or color purposes.

Ford uses a similar system to VW, except, as I recall, it's alphanumeric.



Michael Porter
Roswell, NM

Never let anyone drive you crazy when you know it's within walking distance....

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