Half of Kopf's third reel patent was, again, assigned to Thomas Mills, and this reel was perhaps Kopf's greatest legacy. He described a simple freespool clutch that employed a lever to swing the main gear toward or away from the pinion of a multiplying reel. Versions of his clutch were used by various reel manufacturers for decades, though few could match the beauty of the reel that Kopf made for Mills & Son.

A Mills reel with Kopf's lever-operated
freespool clutch.

Kopf's arrow-shaped lever swings the main gear toward  or away from the pinion.

  The fourth patent was unassigned, and it described what is probably Kopf's best-known design, for a sheet-brass reel foot that was corrugated to fit over the two bottom pillars of a reel. The foot was used on many inexpensive single-action and multiplying reels made by the inventor, many for the Boston retailer John S. Trowbridge & Co.

A single-action and a multiplying reel with Kopf's patented, corrugated foot.

Kopf's corrugated foot on a brass
                 S-handle multiplier. Many such feet on these reels are reinforced with plates soldered below the pillars.