I just bought a new tactic yo-yo from here about a month ago and a piece fell out that went in between the bearing and helped screw the yo-yo back together, don’t know if i can replace it and I’m wondering what i should do?
They are called axles. And they sell them at a fair price on most yoyo webstores. Allthough I don’t belive they sell axles on this site. But I am sure they do on others. Just check. Hope that helped some. 
~James Reed
its actually not the axle, it was this piece that it screwed into on the other side, i probably should have explained that better
So what do you mean? A bearing, axle, responce system, hubstacks, one half of the yoyo.
was it a white ring if it was it was the response
I’m fairly sure you’re talking about the axle. If you’re not, well, this won’t help at all. If you are, you want the 12 mm one: http://shop.yoyoexpert.com/product/197/YYF-Axles
Cool thanks for pointing that out, cause I never knew YYE sold Axles. 
~James Reed
as long as the axle isnt broken just screw it back into the yoyo with your hand. lots of yoyos axles come out sometimes. if it is the threading your pretty screwed but the metal is threaded so.
Maybe your talking about the response. You can buy the YYF response under accessories.