+0
Does anyone know if this is correct? Or should it be '0.500 inches'? If so, why?

This tank’s original shell thickness is less than 0.500 inch; therefore brittle fracture is not a concern per API 653 Sec. 5.3.7
+0
Hi,

If the size is used as an adjective, I'd say 'inch', eg Get the best deal on this 12.7mm (0.5 Inch) Single Digit Numeric Display. (from Google)

If used as a noun (as in your example) I'd say 'inches', eg Some precipitation (0.1 to 0.5 inches) is predicted for Arizona and New Mexico. (from Google)

Best wishes, Clive
Comments  
It should be "inch". I take it to be "half an inch" = "0.5 inch".

Hope this helps.

[Y]
Teachers: We supply a list of EFL job vacancies
Crow3fishDoes anyone know if this is correct? Or should it be '0.500 inches'? If so, why?

This tank’s original shell thickness is less than 0.500 inch; therefore brittle fracture is not a concern per API 653 Sec. 5.3.7
I think that it should be inches, and not inch. The conversion to half of an inch would enable inch, and not inches, but that conversion is not normally made, and is not so here. The singular form inch is applied to unity, as in when there is exactly 1. Here, there is not exactly 1. Whether there are 5 inches or .5 inches, this is not 1, and so is not inch, but inches.
 Clive's reply was promoted to an answer.
The usage .005 inch is absolutely correct. The distinction is simple--for quantities greater than one we use the plural, else the singular. So it's "an inch and a half", but 1.5 inches.
Also, you may note the case where we talk of "a six-inch blade", or otherwise say "the blade is six inches long". Both are correct, though the former one in a way violates the rule.
All the best with your tank and the shell! :-D
Students: Are you brave enough to let our tutors analyse your pronunciation?
To me, 0.50 inches sounds about as good as a bullhorn blown in my ears!How does that logic come about? Besides, the safest expression used universally is a closed quote symbol [ “ ] i.e. 0.5” or 1.0” which will eliminate that question of plurality.