This is what we use for splicing monofilament inside of Dacron or spectra line. The kit comes with 7 different needles. The needles are used with monofilament from 50lb up to 500lb. We insert the end of our monofilament into the end of the needle. It helps if you heat the mono line at the tip prior to pushing it into the needle. It sure is a time saver and makes for clean connections when making wind on leaders or just plain splicing hollow core lines.