hex key

They're really small; most of my RDAs with grub screws fit 1.5mm keys and they're too big, so smaller than that... but I don't know what are standard sizes below it so don't want to guess. I asked VapeNW and they didn't know. I like having extra hex keys when I can. The Griffin and Mutation V4S...

I hope someone can help me. I lost the little hex key for my Aromamizer RDTA velocity style deck. Does anyone know what size it is and where I can find a replacement? I tried 1.5 mm and it is too big.