First, the refill introduction! Black Neutral Core: This product defaults to a 0.5 black neutral pen. (Note: the ordinary refill is not leakproof! The pen needs to be inserted back into the base, otherwise it will leak easily.)        Oil-filled refill (leak-proof): a combination of a gel pen and a ballpoint pen. The ink is more uniform and darker than the ballpoint pen, close to the effect of the neutral core. But the ink is oily, not a pen! (The writing fluency is the best) Ball-point pen refill (leak-proof): A special ball-point pen refill for a table pen, which is different from a general bead core. Its tubing is as thick as the neutral core, and its ink content is several times that of a normal bead core. It is very resistant to writing! Spring head neutral core (leak-proof): a neutral pen for the pen. There are two beads and springs in the pen. When you don't write, the spring will hold the ball on the tip of the pen to prevent ink leakage!