A spring upgrade for US$1? Yes, and it already includes free shipping. This is a promo from eBaybanned for the first 200 buyers so better hurry if you need these. This is actually a spring set comprised of the summer/hardy type for warm temperatures and winter/soft type for cold weathers. Now you've got two springs to use, depending on the season you're playing with your M4 gas blowback rifle. Only fits with the WA-M4 GBB compatible GBB M4 rifles.