This is the Mitsubishi Jetstream ballpoint pen refill, model SXR-38. With a fine 0.38mm ball diameter, it allows for precise writing and provides a smooth writing feel using black oil-based ink. It comes in a 10-pack, making it economical for places where writing instruments are frequently used, such as offices or academies. Please check the compatible pen model (e.g., SXN-150-38) in advance before purchasing.