Like the samurai swords of lore, they have put many countless hours into perfecting the Kwaiback into a knife that is as flawless as they can possibly make it. Hoback Knives pulled out all the stops with this knife! This knife was built with hard work, for hard work. Fully-engineered internal lightening pockets, hardened stainless steel lock insert, HRD (Hoback Roller Detent), hardened stainless pivot, and stainless pivot bearings. The New MK5.1 incorporates some new design changes over the MK5. The bearing washer was removed to simplify maintenance and a slight adjustment was made to the detent to give this Kwaiback a tad bit better action. These are just a few of the things you'll get with a Hoback Knife. The rest you'll just have to see for yourself!

This is what we know from Wiki about the "kwaiken" blade (and by the way, if you haven’t already figured it out, Kwaiken + Hoback = Kwaiback!): 

The kaiken "was once carried by men and women of the samurai class in Japan. It was useful for self-defense in indoor spaces where the long blade katana and intermediate sword wakizashi were inconvenient. Women carried them in their kimono either in a pocket-like space (futokoro) or in the sleeve pouch (tamoto) for self-defense. When a samurai woman married, she was expected to carry a kaiken with her when she moved in with her husband."  "…the kaiken is now called kwaiken (pocket knife). The modern term has no reference in historical records; also called a futokoro-gatana.”

Specifications:

Overall Length: 9.0”(228.6mm)

Blade Length: 3.75"(95.25mm)

Blade Thickness: .187(4.74mm)

Blade Material: Nitro-V *

Blade Finish: Stonewash

Blade Style: Wakizashi Tanto

Blade Edge: Plain

Handle Length: 5.3"(134.62mm)

Handle Material: Titanium Stonewash

Handle Side Thickness: .187(4.74mm) with Heartbeat Design Engraved

Spring Side Thickness: .187(4.74mm) Smooth Titanium

Total Handle Thickness: .58"(14.7mm)

Clip: Tip Up 

Weight: 4.6oz. (130.18g)

Made In USA

 *Nitro V is made by the New Jersey Steel Baron company. They added Nitrogen and Vanadium to improve edge performance, and to achieve high hardness and extreme corrosion resistance.

Other Features:

1. Pivot Thrust Bearings
2. HRD (Hoback Roller Detent)
3. Hardened Stainless Steel Lock Insert With Overtravel Prevention
4. Engineered Internal Lightening Pockets
5. Standard Sizes On All Screws For Ease Of Replacement
6. Cold Formed Bearing Races (Work-Hardened To Increase Bearing And Knife Life)