Why do people say "off" referring to quantity?

[Glade]

I work in Manufacturing and when ordering components, subcontract fabrications etc we always order "3 off" when we want 3 parts.

It has always been this way in every company that I've worked in, but it just occurred to me I don't understand why.

Over to the grammar police

[Glade]

Pioneer said:

Famous Graham said:

Err...it's "of", not off.

As in "3 of part x"

It's a relatively common way to read out an order list as the supplier will be looking up the inventory first (whether by name or SKU/number). So it makes sense for the quantity to follow, rather than precede.

"Part X. Number 123456. 2 of.
Part Y. Number 490559. 6 of."

Yeah but as the OP says a lot of people say 'off', I think it should be 'of'

No misunderstanding - written quotes using "off".
(I find it difficult, I want to use "of" instead)

[Glade]

Holy thread resurrection batman!

Since I last saw this thread I have lived in 5 off houses, done 5 off jobs, 1 off marriage, 1 off divorce and had about 3 off girlfriends.

I thought I'd wasted my 30's but looking back it's been pretty productive really.