The GXL-Knee is a free motion knee joint that is designed to provide extension assist, not prevent knee flexion. In addition, the GXL-Knee has the option of locking at full extension for use as a locked knee joint. Switching between free motion with extension assist to locked is performed by simply rotating the Key Locks. Available with your choice of a 75N, 125N (for standard applications), or 175N pneumatic spring.