Which clamp works best on horizontal seams?

Types of horizontal seam applications

For horizontal seams with .5″ (13 mm) or less dimension of folded portion:

seam profile illustration demonstrating crimping

This illustration demonstrates crimping technique, NOT actual location of clamp.

Option 1: Crimp the seam to 180 degrees at the desired clamp location and use the S-5-E (or Mini). This is easily done with a hand seaming tool with no harm to the seam and actually strengthens the seam.
Option 2: Use the S-5-T or the S-5-S to avoid altering the seam.

For horizontal seams greater than .5″ (13 mm) and less than .625″ (16 mm) dimension of folded portion: Use the S-5-T.

For horizontal seams greater than .65″ (16 mm)

seam profile illustration for horizontal seams

Option 1: Use the S-5-U in its horizontal orientation or the S-5-H90. (Setscrews are tensioned top-down attack).
Option 2: For horizontal seams greater than .65″ (16 mm) but less than .80″ (20 mm) use the S-5-H. (setscrews are tensioned side-attack).

For horizontal seams less than .65″ you may also crimp the seam as shown above for the S-5-E.