DUO System – Frame Connectors

DUO System – Frame Connectors


DUO-System is strategically engineered for fast processing while maintaining a design of traditional frame joint. Simple and easy-to-use. The most common applications are for Bed Rails, Stringers, and Table aprons. We recommend accessories → 2 Flute Straight Router Bit 13/32″ to be combined with —> Router Bushing 1″ OD and the MULTI F Routing Jigs to make make the mortise. Optionally, → Router Base Plate Adapter that holds the Router Bushing 1″ OD.

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DUO-System Frame Connectors

The DUO-System provides the optical qualities of traditional frame joints while being engineered in an innovative manner for fast processing and application. For example, the DUO 100/15 is an ideal frame connector for beds, and, like all KNAPP connectors, is non-visible, can be disassembled, and self-tightening. Beds made with the DUO 100/15 provide the perfect finished look with no visible fastener parts.

The DUO system is non-visible as it is installed in a mortise or rebate using our Routing Jig with a depth of 13 mm and milled either into the end-grain or face of the wood component. The DUO-System connector consists of two identical connector parts, made of high strength blue-galvanized weather-resistant steel, and is manufactured in Austria.

The choice of the correct DUO connector size depends on the used timber dimension. The milling operations can be made optionally with a hand router or a CNC. It is so quick and easy to assemble that even the end-user can do it, and with 8 different sizes, you will be sure to find the exact size you need.

Features and Benefits:
  • Fast assembly
    • Efficient and very good to use in production line manufacturing.
    • Components are simply hooked together in seconds
    • Reduces labor and equipment cost
    • Efficient: High degree of pre-manufacturing.
    • Components can be transported and simply assembled on site.
  • Non-visible connector
    • Appeals to the architect and customer
    • Concealed
  • Self-tightening
    • Adjust with the included pan head screw to desired tightness
    • Can be disassembled and reassembled
  • Versatile
    • The wood component can shrink and swell, while the joint can be adjusted and re-tightened via the screws of the fastener.
    • Safe and tested by HFA (Holzforschung Austria)
  • Perfect for industrial manufacturing with CNC
  • For handheld routers, use the Routing Jig for a perfect installation every time.
  • Used with all wood and board materials
  • Tables and chairs
  • Bed frames
  • Stairs i.e. stringer to post
  • Columns and beams
  • Booths and pews
  • Interior design
  • Small timber construction
By screwing with CS-screws Ø 5 mm or Ø 6 mm (Length as required) and PH-screws Ø 5 mm or Ø 6 mm
Concealed, self locking, by adjustable screw connector, for frame connections
With CNC-Machine, Long hole drilling machine, Hand router
Suitable materials
All solid and plywood materials from 21 mm
Frame connections for furniture, stairs and Stand construction to Interior design





Furniture and Interior Design


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Load values

Note* The load value refers to the transverse force in the insertion direction.

Details of the stress values are of the certificate of Holzforschung Austria from 02.11.2000 and the current KNAPP catalogs. For commercial use of the DUO-System, according to Ö-Norm M5027, CS-screws (5×40, 5×60, 6×40, 6×60 mm) should be used.

F0 0,86 kN*
DUO 46/15
F0 0,97 kN*
DUO 26/26
F0 1,29 kN*
DUO 62/15
F0 1,30 kN*
DUO 46/30
F0 2,00 kN*
DUO 100/15
F0 2,15 kN*
DUO 62/30
F0 2,37 kN*
DUO 90/20
F0 4,35 kN*
DUO 90/46


(View and Download Instruction Manual)


  1. Cut the mortise by means of a → 2 Flute Straight Router Bit 13/32″ to be combined with —> Router Bushing 1″ OD and the MULTI F Routing Jigs. *Note; please pay particular attention when choosing a MULTI F Routing Jigs. The size of the Routing Jig will depend on the size of the connectors. Optionally, use the → Router Base Plate Adapter to hold the Router Bushing 1″ OD.
  2. Use the MULTI F Routing Jig to perfectly align and mortise either the end-grain or face 13 mm deep. Mortise width is preset via the Routing Jiga and mortise length depends on the size connector. Please download Instruction Manual for a particular connector size. See above or under mein tab Resources → Instruction Manuals
  3. Set the one DUO-System connector plate into the mortise, using it as a jig to predrill holes.
  4. Attach one DUO-System plate with the screws provided
  5. Lay the second plate over the first and screw in the pan head screws until they are snug against the second plate. (this will set the correct depth of the pan head screws and ensure a tight fit during final installation)
  6. Install second DUO-System plate with the screws provided
  7. Attach workpiece using a rubber mallet


  1. The joint is always tight, as the connector snaps together in a dovetail-like manner. Still, the fasteners allow the natural shrinking and swelling of the joints and are adjustable if needed.


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