HPA Adapter for EU-Series
Feeds from MP5/SMG-5 AEG magazines
US-Spec HPA Line connector 
If you want to run your SSP18 or EU-series GBB on HPA, the Novritsch HPA SMG-5 Magazine Adapter for EU Series GBB Pistols; Gen 2 is the easiest way to do it. This adapter is pre-built using a zinc alloy magazine body and fibre-reinforced nylon polymer adapter and is outfitted for US Spec HPA lines by default. This adapter is designed to feed from curved MP5/SMG-5 AEG mid-cap magazines and HPA from an external tank (not included), increasing capacity considerably and practically eliminating FPS fluctuation due to the "cooldown" effect. 
The adapter is pre-assembled, meaning you don't need to mess around putting it together or run the risk of doing it wrong and causing injury. Naturally, you'll need an HPA bottle, air line and regulator to use this adapter and the fitting is US Spec, meaning only US Spec air lines will fit. If you're running your SSP18 in the Novritsch Minimalist Carbine Kit or as a primary, the Novritsch HPA SMG-5 Magazine Adapter for EU Series GBB Pistols; Gen 2 will give you the rapid-fire performance and capacity you need to stay ahead!