The spring is in the majority of airsoft guns today which is partly how to determine the guns power limit. Its the part that post people would usually switch out for something stronger or weaker for CQB.
ARES are a well known brand in the Asia market today due to their affordable AEG and sniper rifles. They've been making airsoft guns for awhile and know what the market wants when it comes to affordable yet quality cost guns.
The C.P.S.B. Upgrade Spring is part of a series of spring they've released which is designed only for the ARES Amoeba Striker system, so please refrain from installing into other platforms.
Items included:
1x ARES Amoeba Striker C.P.S.B. Upgrade Spring - 550