the new 510 flat tips I've been getting from Nhaler have 2 air slots and work great with a full PTB. A little more flavor. the end dosen't seem like it can pop out(but maybe it can)- I haven't tried hard. He dosent sell blank one, but there still worth it. I like the bite. I immediatly rip out the polyfill and replace with PTB. I have been using one of my PTB filler (washing every other day) for 3 weeks now, and it shows no signs of wearing out. The end that hits the atty was just barely showing signs of fraying (like .5 mm) allmost nothing- I just trimmed it off. These don't come apart like fluval or poly. They are woven so it dosen't fray easilly. I love em'.