gas spring,chair gas spring,office chair gas spring,gas cylinder,gas strut gas spring,chair gas spring,office chair gas spring,gas lift, ... . Function:Height adjustment,up and down freely,no noise,swivel freely3. Surface finishment: powder coating/chromed4. Bottom Type: ... . Certificate: ISO9001 + SGS BIFMAX 5.1(Impact testing,swivel testing,fatigue testing,back strength testing,bushing testing) + TUV ...