Oajen gas cylinder for office chair 4" stroke black, fits most office chairs 4" stroke heavy duty gas cylinder for office chair. Fits most chair base with 2" opening in the base. Exceeds BIFMA quality. Made in Taiwan. This gas cylinder is designed for use with larger person of up to 250 lbs. For 3" stroke, http://www.amazon.com/gp/product/B007ZT4A7S For 5" stroke, http://www.amazon.com/gp/product/B007ZT4HE4