All Ultra Tungsten products are 97% pure tungsten positioning them amongst the worlds smallest weights. There are no inserts to possibly interfere with or fray your fishing line. The line holes on Ultra Tungsten worm weights are rounded and polished smooth at both ends to minimize any line friction. Ultra Tungsten worm weights are available with or without a locking screw. Of course, the ones without the screw can be pegged in place with an Ultra Peg.