These monofilament tighteners are used to easily tighten our deer fence monofilament wire for the best looking and most effective installation possible. By inserting a length of monofilament wire into the groove in the tightener, the line may be tightened by slowing rotating the tightener with the tightener tool and shortening the line. Each monofilament tightener is ultra-violet (UV) treated for increased longevity. We recommend using two monofilament tighteners between each corner of your fencing project, one each for the top and bottom monofilament wires. You will need our monofilament tightener tool to properly operate these monofilament tighteners.