The Difference Between Nail-Up and Drop-In Tiles

The difference is the edge and size.  The nail-up tiles are larger 24 3/8" x 24 3/8" and the edge usually comes with dot and dosh overlap.  Drop-in tiles are 23 7/8"  x 23 7/8".

Example of a Nail-Up Tile

Example of a Drop-IN Tile