Freebase nicotine shots are designed to be added into shortfill e-liquids in order to add a nicotine content to an otherwise nicotine-free vape juice. This is because shortfills come in bottles larger than 10ml, and so are sold without nicotine in line with UK regulations. A shortfill will usually leave enough room in the bottle for the addition of enough nicotine shots to create a 3 mg/ml strength overall, for example a 50ml shortfill will come in a 60ml bottle, leaving room for one nic shot, while a 100ml shortfill will come in a 120ml bottle, leaving room for two nic shots.
To add your nic shot/s just remove the cap and nozzle from all of the bottles and empty the contents of the nic shot/s into the short fill. Replace the cap and nozzle on the shortfill and shake to combine. The e-liquid is then ready to use straight away.