Otter Handmade D2 Tool Steel Original Filipino Balisong Butterfly Knife with Brass and Jigged Bone Handle | 24cm EDC Flipper Gift for Him | BF-91

The BF-91 Otter is a 24cm balisong with a 12cm D2 blade, 180g, brass with jigged bone inserts. An otter is never still in the water, so this is the page where we deal with water properly, because D2 is described as semi-stainless and most people have no idea what the “semi” is doing there.

Semi-stainless is a real category, not a hedge

The convention is that a steel counts as stainless at around thirteen percent chromium. That is the point where enough chromium is available to form a continuous protective oxide layer on the surface.

D2 carries eleven to twelve percent. It is close, and close is not the same. What that means in practice is a steel that will happily ignore humidity, rain and a wet afternoon, and that can still spot if you push it, where our 440C and VG10 knives will not.

Most of the chromium in D2 is also locked up in carbides rather than dissolved in the steel around them, which is what gives it the edge retention and also why the free chromium available for corrosion resistance is lower than the headline number suggests.

What actually causes trouble, ranked

The row people get caught by is the second one. Nobody thinks of their own hands as a corrosion risk, and a long flipping session leaves a film of salt on the blade that sits there until you wipe it.

If it has spotted

Light orange dust that wipes off is surface rust caught early. Oil on a cloth and firm pressure removes it and nothing is lost. Established rust that does not wipe off wants a fine abrasive with oil, worked gently, then oiled again. Dark pits left behind afterwards are permanent, because the steel there is gone.

Do not use a wire brush or a rotary tool. They remove far more steel than the rust did.

Jigged bone, and why the texture matters here

Jigging is a cut pattern worked into the surface of the bone rather than a print or a coating. It has been done on knife handles for well over a century for one practical reason: a textured handle holds in a wet hand and a polished one does not.

That pairs neatly with everything above. If your hands are wet or your session has been long, a polished horn handle becomes genuinely slippery and jigged bone does not. It is the most secure grip surface in the range.

It will warm in colour over the years and it will not match the photograph, because bone takes finish unevenly by nature. Uneven colour is bone. A crack or a loose insert is our problem and we will fix it.

D2 steel at 58-60 HRC on this balisong, and the trade

The best edge retention we sell, by a clear margin. In exchange, sharpening wants a diamond plate and takes its time, because the carbides that resist wear are harder than the abrasive in an ordinary ceramic stone.

We heat treat to 58-60 rather than higher, because a carbide-heavy steel at 62 chips when the knife hits a floor. At 59 it rolls, and a rolled edge is recoverable.

The frame of this D2 balisong

Twenty-four centimetres open at 180g, brass bolsters with the bone inserts. The standard size at the weight most owners settle on: enough momentum that a rotation carries itself, not enough to tire your arm across an hour.

Ordering this D2 butterfly knife

Unsharpened trainer, chosen above Add to Cart. Everything on this page about water applies to it identically, since a blunt D2 blade corrodes on the same schedule as a sharp one.

Leather sheath included, cut to the frame. Free delivery within the States, $49 flat anywhere else however much is in the box.