Significance of an "X" suffix in an M-series truck's serial number?

[studerex]

Fish plate is the heavy plate added to the frame to give it more strength.

I wonder where that term came from.

[Rerun]

According to the Oxford English Dictionary, the name is derived from fish, a wooden bar with a curved profile used to strengthen a ship's mast.

[migral23]

Yes, Richard, I can confirm that the M16 I've been referring to (not mine yet; still in negotiations) is reported to have a two-speed rear (according to its current owner's written description).

[Studebaker Wheel]

Yes, Richard, I can confirm that the M16 I've been referring to (not mine yet; still in negotiations) is reported to have a two-speed rear (according to its current owner's written description).

Well then that settles it!!

[migral23]

Richard, I noted that you said you have original documentation regarding the M16's two-speed rear option, and that it would be available "if anyone is interested".
Yes, I'd be interested. I'm working on the premise that I will become the owner of the truck that prompted this whole discussion thread.
Should I p/m you about how to get the information ? Thanks, and thanks for your research !

[Studebaker Wheel]

See page from Service Bulletin #189 - June 1947 below.

[Skip Lackie]

Upon further review I am now thinking that the X suffix is likely for trucks equipped with the two-speed vacuum shift rear axle. This feature was introduced in mid April 1947 at serial M16-41305. The original invoices I have with the X suffix are all after that date and I see no such X suffix on invoices before that date. Now if Mike will simply confirm that his truck (M16-51492) does indeed have the two-speed rear axle I will be convinced (sort of). If it doesn't it is back to square one! Have original documentation on the two-speed option if anyone is interested.

Richard-
A minor point, but it might be worth noting that 2-speed axles were available on M16 trucks before that date. The significance of the changeover (as indicated by the service bulletin excerpt you posted) was that the new ones were hypoid type, which required a different lubricant.

I do agree with your conclusion on the meaning of the X suffix. But to follow up on my earlier posting on the use of suffix letters to indicate weight class, here are a couple of excerpts from truck service letters regarding shipping weights of trucks sold in Pennsylvania, dated March 19, and April 15, 1946:

"The first letter of the double symbol after each model designates the weight classification of the chassis less cab, and the second letter, the weight classification of the chassis with cab."

"Also use symbol M-16-95-UV if chassis is equipped with one extra 30-gal. gas tank or a 2-speed axle in addition to the above equipment and one of the following optional tire combinations . . . . "