I have two bikes one has a 7/8" stem and the other has 1 1/8" stem. I thought they only ranged from 1" to 1 1/8"?
Wahts going on

Old-style "quill" stems are measured by the diameter that fits inside the fork's steerer tube. Stems for threadless forks are measured by the outside diameter of the steerer. Since there's at least 3 common diameters of steerer: 1", 1 1/8", and 1 1/4", there's at least 4 possible measurements that could be stated.

A 7/8" (22.2mm) quill stem would fit in a 1" fork. To make life even more interesting, 1" steerers came in different wall thicknesses, necessitating different stems. 13/16" is common on cheaper bikes and old Schwinns and 22.0mm was the old French standard.

Confused yet?

One of the most important bike-tools to have is one of these:



And please refer to this Park Tool - headset standards site. It'll all make sense after that.

As Jeff said, quill stems go inside the steerer tube so they have to be smaller than the nominal outside diameter. Since the wall thickness on 1" steerers vary, there are three nominal 1" quill diameter but 22.2 mm is by far the most common.

BTW, 1-1/8" quill stems (for 1-1/8" steerer tubes) are also available and measure a true 1" (25.4 mm) in diameter but these are not real common. Also, there were a very few 1-1/4" steerers but you are unlikely to ever come across one of these.

Threadless stems fit outside the steerer so their inside diameters match the OD of the steerer and are truly 1" or 1-1/8".

1 1/8" quill is quite common on beach cruisers.

The older Schwinns commonly had 21.1 mm (7/8") quill stems. A few other brands used them at times as well.

I just bought a 21.1 mm quill to 1 1/8" adapter for $10 US on ebay. It was totally worth it. Fussing with 7/8 stems is a pain in the butt. If the stem on the bike works well for you, leave it alone. If' you need a different stem, I'd get an adapter. Mine was under the brand "Kruzer Kitz". The only other good option for ditching the 7/8 stem is to get a new fork and headset locknut that are 22.2 mm.

Yes, and it used to be common on MTB's until the mid-90's when the threadless revolution blew them away. So, if the OP is working on Beach Cruisers or old MTBs, a 1-1/8" quill may be a common item.

21.15mm quill stems, aka .833", equals 5/6." 22.2mm quill stems, aka 7/8", are the most common size for one inch forks.

21.15mm equals 5/6 inch. 22.2mm equals 7/8 inch.

Those are the actual measurements. But a 22.2 mm stem is referred to as a 1" quill. A 25.4 is considered a 1 1/8' quill and so forth. My older Takara was stamped 7/8" and then right underneath stamped 21.1 mm.

EDIT: Misread what you're were actually saying. That's funny. I wonder why my stem is stamped with both. Maybe 7/8" refers to something else?

The 21.15mm stems (like the ones commonly found on old Schwinns) are almost always stamped .833. As for a 21.15mm stem stamped 7/8, I have no idea.