The Maxi-Ject Needles are used on the end of the Maxi-Ject Darts. The Maxi-Ject Blowpipe System (sold separately) by Addison Labs enables you to easily and economically inject a wide variety of animals remotely without the trauma of other systems. The needles have side holes and a silicone sleeve that slides over the holes to prevent any leakage. 19 gauge 5 Count