Glass Inserts: A hyper-smooth small diameter insert designed for extra fine tying threads, 8/0 and above, as well as synthetic threads. Ultra slick! Delrin Feet Comfort Grip 400 grade stainless steel Available in three sizes: 3", 4", and 4.75" Glass Inserts: A hyper-smooth small diameter insert designed for extra fine tying threads 8/0 and above as well as synthetic threads. Ultra slick!,Delrin Feet,Comfort Grip,400 grade stainless steel,Available in three sizes: 3" 4" and 4.75"