This item is the #1915 E-Rotary in a Super UV plastic head.  This model comes with a barbed hook and a 1/2 inch high fin on the back.  Other models come with barbless hooks (2300 series) and still others come with larger fins for bigger bait.  The Rotary series baitholders are tops for catching salmon.  You cannot beat the perfect rolling and wiggling action as they are trolled.  They have a diagonal fin on the back that gives your bait a perfect roll.  The hooks are spaced at the back of your bait so you don't miss hookups.  These 1900 series bait holders are for baitfish 4 to 5 inches long.  The diagonal fin on the back that causes the rotation is 1/2 inch high. The hook is a 5/0 stainless siwash.  It is best not to place the hook into the bait.  Let it swing free.  This allows the bait holder to spin with more erratic wounded fish action.  For 6 to 7 inch bait you should use the Big Fin series. For barbless hook models, call up the Roto Chip #2300 series.
To mount bait in the Roto Chip holder, slide the wire clamp toward the front of the holder.  The holder will spring open.  Lay the bait in the jaws and slide the clamp to the rear until the baitfish is held in place. The most popular Roto Chip colors for salmon are clear, red and chartreuse.  If one color is not catching fish after 30 minutes or so, try another color.  On some days one color will dominate all the others.  The stainless tube in the front of the Roto Chip is the electronic EChip.  As the baitholder rotates, the EChip discharges a tiny electric pulse that exactly duplicates the nerve pulse of a wounded baitfish.  This results in more fish and bigger fish.  The EChip never wears out.  To learn more about it go to www.protroll.com and call up the EChip.