For Uni-ball Jetstream 4 & 1, Extra Fine Point Roller Ball Pens Refills -0.5mm Ball Point-black/blue/red/green Ink +Diamond Infused Leads [Nano Dia-40 Leads] 0.5mm Hb Value Set It is a set of the spare Refills &Leads made specially for those who own Jet Stream 4 & 1. Keep in mind that it does not fit normal Jet Stream. It is smooth and they are a spare lead which cannot break easily, and the profitable set which attached Nano Daia (hot product of Uni) together.(HB 40 Leads)