Sunstar Bung Knock Free Metal Review: A No-Knock Mechanical Pencil That Surprised Us

Introduction

The Sunstar Bung Knock Free Metal is the newest entry in Sunstar’s Knock Free line of mechanical pencils, released in late August 2025 at a price of 1,650 yen. Its headline feature is an automatic lead-advance mechanism: you knock the pencil once to extend the lead, and after that it feeds itself as you write, eliminating repeated knocking entirely.

The verdict up front: this is a fatigue-friendly pencil built for long writing sessions, which makes it a genuinely good fit for studying, work, and standardized-test practice. It is also more thoughtfully finished than we expected at this price. Here is what stood out during hands-on use.

First Impressions and Design

The pencil arrives in a paper box with a cushioned insert that holds it firmly in place, which is a nice touch at this price point. One caution: the insert is cut through from both sides, so the pencil can slip out of the back if you lift the box while opening it. Open it flat on a desk rather than in hand.

Our first impression was that it feels lighter than expected. The line-up includes six colors in the 0.5mm lead size only: Matte Black, Matte White, Matte Blue, Metallic Red, Silver, and Metallic Navy. The silver model we tested has a sparkle-flake metallic paint with a slightly coarse texture, similar in character to the Graf Gear line. The clip is black on every color, which helps a set of them look cohesive on a store shelf.

Fair warning: the product photos suggest a heavier, more luxurious feel than the real thing delivers. If you are imagining a weighty, premium metal pencil, temper your expectations.

Feature 1: The Assisted Grip Lines

From near the base of the front cone toward the center of the barrel, there are three long assisted grip zones, two strips per side, positioned to cover the three fingers of a standard tripod grip. Before using it, we assumed being told where to hold the pencil would feel restrictive. In practice it barely registers.

The grip material is not rubber, has almost no raised texture against the fingers, and does not stick to the skin. Zoom in and you can see fine rectangles arranged in rows, likely resin, with just enough relief to help. Even gripping outside the zones works fine, and the slightly textured paint keeps the barrel from feeling slippery. There is no tackiness at all.

Feature 2: One-Knock Auto Lead Advance

This is the defining trait of the Knock Free series. A single knock extends the lead, and from then on the mechanism feeds lead internally as the tip subtly moves up and down during writing. Even when it looks like the lead has retreated, writing continues without a problem. Notably, Sunstar has not slapped a branded marketing name on the mechanism, which we appreciated.

The front cone is metal with an elongated rectangular profile and a short tip, a step up from the resin tip on the previous Knock Free. Internally, the tank is resin, the knock cap is resin, and the pencil should not be disassembled further. The overall balance sits low in the hand, and at 144mm long, 13.4g, and a 9mm grip diameter, it is compact and easy to control.

Feature 3: Direct Lead Loading

Our favorite surprise: you can refill the lead directly through the knock cap without removing it. Taking the knock cap off to reload is never truly difficult, but it is always mildly annoying, and this neatly solves it. The cap can still be removed if needed, though there is no eraser underneath.

One quirk of the previous Knock Free was that you knocked via the clip. Here you knock normally, and the knock is nearly silent with very little travel, which suits a mechanism you will rarely need.

Writing Experience

The auto-advance mechanism means the tip moves slightly up and down as you write, so you will feel a faint rattle during use. That is inherent to the design rather than a flaw. There is also no cushioning mechanism this time, unlike the previous model, and the included lead felt scratchy, so swapping to a 2B lead smoothed things out considerably.

Once dialed in, the writing feel is genuinely pleasant: light, well balanced, and stable, with low fatigue over long sessions. Getting this level of refinement for under 2,000 yen is impressive.

Things to Consider Before Buying

A few trade-offs are worth knowing before you buy. The clip, while thin and reasonably easy to clip thanks to its upturned tip, tends to press into your hand during writing and is a genuine annoyance. The grip zones, though easy to live with, will divide opinion. And the auto-advance mechanism changes the writing feel compared with a conventional pencil, so if you dislike that character, this is not your pencil.

Finally, storing it in a pen case without a holder can let the lead extend on its own while moving around. That is the fate of any auto-advance pencil, but it is worth planning for.

Buying Advice

If you write for long stretches, study regularly, or want a quiet, low-fatigue pencil for exams and work, the Knock Free Metal earns its place. If you prefer a heavy, premium-feeling barrel, or a conventional fixed-tip writing feel, look elsewhere. For everyone else, the combination of the auto lead advance, direct lead loading, and solid build quality at 1,650 yen makes this an easy recommendation and one of the more original pencils released this year.

Conclusion

The Sunstar Bung Knock Free Metal is stylish, practical, and more polished than expected from a brand known for broad general-audience products. The direct lead loading is the feature we most want to see spread across other models. If any of this sounds appealing, it is well worth a look.