Note that the carbide spheres on the top of the plate are in different positions. See illustrations, below:

TL1 Plate

This is a TL1 adapter plate.  Note the side-by-side position of the two carbide spheres at the 12 o'clock position. This plate fits TL1 probe heads. 

TL2/TL4 Plate

This is a TL2/TL4 adapter plate.  Note the single carbide sphere at the 12 o'clock position. This plate fits TL2/TL4 probe heads. 

TL3 Plate

This is a TL3 adapter plate.  Note the space between the two carbide spheres at the 12 o'clock position.  This plate fits TL3 probe heads.