V2 Model Pen has the "injecthru" feature with a hole and a retractable ring on the pen cap end. This allows for sight-free needle administration. For researchers with needle apprehension, this unique feature will conceal the needle during administration. They only come in the 60-unit standard version. 5 V2 Pens (Red, Blue, Green, Purple, Silver) 10 - 3ml individually wrapped empty Cartridges