i just bought these 901's from Totally wicked and the little o-ring that keeps the contact post from touching the little base plate is gone on one of them, keeping it from firing. i know it works because i took a nail and pried out the center post a little, then screwed it down on my v2 slowly(button depressed) and it fired. so yeah, if someone could plz tell me the size o-ring i need, that would be awesome.