Connect 3/8" tubing to 3/8" tubes with the three eighths by three eighths coupling

Connect 1/2" tubing to 3/8" tubes with the half by three-eighths coupling

Connect two 1/2" tubing pipes with the half by half coupling

Connect 1/2" tubing to 3/4" tubes with the half by three quarters coupling

Connect 3/4" tubing to 3/4" tubes with the three quarters by three quarters coupling