Tall bald this should help you. 3/16" would be way to long. it should below 1/8" closer to 1/16" The hole on the side actualy reaches over to the shaft hole on the tool.
Instructions:
Push the rivet threw the hole then turns the material over. Place the burr or washer on the rivet, then use the rivet setter’s straight hole to drive the burr down against the material. Cut the rivet off close to the burr with side or end nippers. Do not cut off flush with the burr, but leave about 1/16 of an inch above the burr. The hole on the side of the rivet setter can be used to dislodge any waste that is wedged into the tool. Place the concave recess of the setter on the burr. Hold perpendicular and strike the end of the setter forcefully, turning to the left then right as you strike. This spreads the end of the rivet over the burr simultaneously rounding its end. A few extra blows from a soft faced mallet can be used to flatten the rivet end a bit, if desired.