Bad idea: 26-inch tires. No, not the tire, but rather the designation.

For a good time, see Sheldon Brown's tire sizing chart and Bike Works NYC tire sizing chart (both as of 2015/01).

So far, we have:

• 26x(decimal number) = ISO 559 aka "mountain bike". Many sizes.
• 26x(fraction) = ISO 571 aka 650C aka S-7 aka F9.  Fractions include 3/4, 1, 1-3/8, 1-5/8, 1-3/4.
• 26x(fraction) = ISO 584 aka 650B aka S-4.  Fractions include 1-3/8, 1-1/2, 1-5/8
• 26x(fraction) = ISO 585.  Fractions include 1-1/2, 1-3/8.
• 26x(fraction) = ISO 590 aka E.A.3 aka English 3-speed aka 650A.  Fractions include 1-3/8, 1-1/2.
• 26x(fraction) = ISO 597 aka S-6.  Fractions include 1-1/4, 1-3/8.
• 26x(decimal number) = ISO 599.  Note this is 599 not 559, which is also a "26 inch" size.  Decimals include 1.25 and 1.375
• 26x1-1/2 = ISO 607.

Some of these won't fit at all on the wrong rim. Some, like ISO 584 and ISO 585 can probably be interchanged freely. Yet others, like an ISO 590 tire on an ISO 597 rim may be possible to mount, but never to get round, while ISO 597 tire on an ISO 590 rim may seem to fit and then blow off.

I'd like a 26-inch tire.

I'd like A 26-inch tire. Not a confusing array of incompatible 26-inch sizes with similar names.