arbor - any of various rotating shafts that serve as axes for larger rotating parts
mandrel, mandril, spindle
drive - (computer science) a device that writes data onto or reads data from a storage medium
rotating shaft, shaft - a revolving rod that transmits power or motion

arbor - trn, vreteno, vratilo, valjak, osovina
(Milićević J, Rečnik mašinske tehnike en-sr)

Možda je "arbour size" veličina otvora za osovinu (na kotačima i prirubnicama) u koji se stavlja (umeće) vreteno (spindle) pogonskog alata (power tool). Samo nagađam, trebalo bi znati i širi kontekst...

A možda i ovo može pomoći:

"From Wikipedia, the free encyclopedia
(Redirected from Arbour (tool))
...
A mandrel (pronounced /'mændril/, and also spelled mandril; in American English also called an arbor) is either an object used to shape machined work; a tool component that grips or clamps materials to be machined; or a tool component that can be used to grip other moving tool components."
( http://en.wikipedia.org/wiki/Arbour_(tool) )


"Watch Glossary
...
Arbor:
The spindle, shaft, or axle upon which the wheels of a watch train are mounted."
( http://www.tourbillonwatches.com/glossary.html )


"IRWIN Industrial Tool Company - Tool Tips > Glossary
...
Arbor - a shaft driven by a tool's motor that turns blades or other cutting tools. Also called a mandrel."
( http://www.irwin.com/irwin/consumer/jhtml/glossaryList.jhtml... )


"Dictionary
...
arbor - A part of a mechanism that rotates or that turns in pivot bearings while holding something that turns. An example would be the mini mandrels when in a flexshaft handpiece."
( http://www.fdjtool.com/custom.aspx?id=17 )