Yes, generally speaking most 10.5" reel machines will play 7" reels as well. There is typically a large / small reel switch to adjust tape tension and braking force for the 2 sizes. You have to remove the large hole NAB hub adapters. In addition, the head configuration must be correct for the tape to be played as well as the speed. Pre-recorded tapes come in 3 typical varieties. The oldest are 2 track at 7.5" per sec. (some of the very early ones were for "staggered heads" and are not easily recovered on a modern machine - "stacked heads" is the term for normal old 2 track) Then they went to 1/4 track, sometimes called 4 track, and in the later years to 3 3/4" per sec. speed. Other variations exist such as 4 channel quadraphonic and Dolby encoding but they are more rare.
Some pro studio machines used reels up to 14" in diameter and some miniature pocket recorders used reels smaller than 3".
3",5",7", and 10 1/2" are the most common sizes.
More info exists in the sticky "Beginners guide to Tape Recorder Basics" under "General Discussion" on this forum.
