Coupling systems of drain cleaning cables

The manufacturers of drain cleaning machines use different coupling systems for their drain cables. The most common is the T-Nut system, followed by the square system. Drain cleaning cables for manual operation often have a thread.

Drain cables with T-Nut coupling

As the name "T-Nut"-coupling indicates, such drain cleaning cables have a female or negative coupling with a T-shaped indentation. The negative T-Nut is located at the end of the drain cleaning cable, that is, at the end of the drain cable, which looks out of the pipe. The corresponding positive coupling is T-shaped in the profile and has a spring-loaded locking pin that protrudes from the T-profile.

The T-Nut has a bevel on one side. From this side the T-profile is pushed in from the side. The bevel causes the pin of the positive T-Nut coupling to be pressed in when coupling, so that it then engages in the hole in the negative T-Nut. It is essential that the pin engages correctly, as only then is the connection of the drain cables secured and cannot become loose. Drain cleaning tools always have a negative T-Nut coupling and are coupled using the same procedure.

To release the connection, a pin key or a small screwdriver is necessary. This key is inserted laterally into the cross hole of the negative T-Nut coupling and presses the locking pin downwards so that the drain cable can be pulled out again laterally.

The T-Nut coupling system is very reliable and widely used. It is used by ROTHENBERGER, rak, ROWO, REMS, VIRAX, RIS and also RIDGID. Its weakness is that the locking pin must always engage, otherwise the connection will easily become loose. If the pin is rusty and does not run properly, if the spring is broken or if the hole for receiving the pin in the negative T-Nut coupling has a burr or rust, the locking pin does not engage correctly. It is therefore always necessary to pay close attention and test whether the clutch is engaged correctly. This can be done by shaking or better by a lateral view into the cross hole of the negative T-Nut coupling.

The T-Nut couplings are manufactured with 16mm (5/8" inch), 22mm (7/8" inch) and 32mm (1.1/4" inch) diameter. All compatible drain cables and drain cleaning tools are specified with this size. For example, a bulb auger may have a diameter greater than 16mm, but the tool is still referred to as "bulb auger 16mm".

Drain cables with square coupling

The other common coupling system is the square coupling. Here the female or negative coupling has a square recess. At the side, one of the coupling edges is drilled round to accommodate the locking pin. The female coupler is also here the rear part of the drain cable, i.e. at the end that looks out of the tube.

The positive square coupling has a spring-loaded safety pin that protrudes laterally. This is pressed in during the coupling process and snaps into the hole provided for this purpose in the negative square coupling. The advantage is that it is immediately visible from the outside whether the pin is correctly engaged.

To release the connection, the lateral locking pin must be pressed in with a suitable key or other tool. The square coupling can then simply be pulled apart.

The square coupling system is used by KaRo® or Rioned®. It is found in all drum machines of these manufacturers. Square couplings with 1/4" inch size are used in drain cleaning cables with 10mm (3/8" inch) diameter, square couplings with 3/8" inch are used in drain cables with 13mm (1/2" inch) and 16mm (5/8" inch) diameter and square couplings with 1/2" inch size are used in drain cables with 20mm (3/4" inch) diameter.

The tool sizes of the drain cleaning tools are simply stated by us in the size of the corresponding drain cable diameter to which they fit. This is then for example " bulb auger Ø30mm square coupling 3/8" for 13mm & 16mm drain cables".

Drain cables with threaded coupling

Simple drain cleaning systems such as pure hand drain cleaning cables, some of which have a threaded coupling. Our hand pipe cleaning spirals from E&R are made with a 1/2" inch WW thread. Other manufacturers also use metric threads.

The thread coupling is very easy to use, the drain cables or extensions are simply screwed together. Similarly, drain cleaning tools are screwed on. The couplings have no safety device. Their major weak point is that they screw on when operating in left-hand mode. If this is not taken into account or forgotten, the tool or drain cable can become loose in the pipe!

Do you still have open questions about the different couplings of drain cleaning cable, or do you need further help in selecting a suitable drain cable? Simply write to us via our  contact form, we will be pleased to help you!