"One Of" or "One Off"
 

If it is one of a kind why isn't it "one of" instead of "one off" ?

I've seen both used interchangeably.

I believe it is like comparing apples and grapes. If u continue the sentence as one of them to one off them they give different meanings. Similarly one of and one off are totally different in meaning. One of belongs to the rest whereas one off is custom made. Use of language can get distorted with overuse. Does that make sense?:)

I made it right in between running changes to the assembly line, so it is a one off.

I made a bunch in different colors later on, and this red one is one of the one offs.

This explains it well:

http://www.nytimes.com/2010/07/04/magazine/04FOB-onlanguage-t.html

One off is of British origin, meaning that something is unique.
You could also have 3-off, 6-off, etc, meaning that these 3 (or however many) items are identical, but as a group are unique from all others ever made.

One of a kind means the same thing as one off.

One of three, or one of six, may or may not mean the same as 3-off or 6-off. One of three, for example, merely means one from a group of three. There is no express uniqueness in the phrase, though it may be implied from the context.

edit: nevermind... Graham's link does the trick.

This certainly makes a lot more sense than those guys from "Speed" stating a "Frame Off Restoration" on an obvious unibody vehicle.

This thread here has me heading to the cabinet to pour up a coconut rum! I swear I've heard them both all my life and never thought about this.

Hallelujah

One of 100

One off from the rest...different from the rest