Ringfeder RfN 7110 Compact Locking Assembly, 8-130 mm

Compact self-centring assembly with screws outside the clamping area

The RfN 7110 is a specially small-dimensioned, self-centring locking assembly without axial displacement of the hub. Its locking screws sit outside the clamping area, and surface pressures stay relatively low, so the hub can be built economically small. The low structural height makes it fit in narrow spaces, and sizes start at 8 mm and run to 130 mm shaft diameter, with torques from 30 Nm to 23,700 Nm.

The table gives a collar diameter DB1, a diameter D3 and a screw pitch circle d1 for every size, together with lengths L, L1, L4 and L8. Weights run from 0.06 kg up to 14.58 kg.

Technical specifications

Selected sizes from the tech paper

The table holds 39 sizes. Besides the usual columns it gives collar diameter DB1 and the length L4 from the collar.

Design-in notes

Pressures on the shaft run from 85 to 230 N/mm2 and on the hub from 70 to 135 N/mm2; the low hub pressure is what allows a thin-walled hub, and the tech paper names thin hubs with a low extension limit as a typical use. The 70 x 90 size, for instance, transmits 4,330 Nm and 123 kN with 8 M10 screws at 83 Nm; its collar is 119 mm and the screw pitch circle 101 mm.

A stainless steel RfN 7110, for machinery that must be cleaned intensely, has its own torque table in the product paper. For the very smallest shafts it competes with the RfN 7061, which is a plain two-piece design without a collar; choose the RfN 7110 where the collar and the screw location outside the clamping zone are an advantage. Shaft h8, hub H8, Ra 1.6 um. Confirm before ordering: space for the collar, hub thickness, torque, and whether a stainless steel version is needed.

Shaft and hub can be kept small because no keyway weakens them, which allows light, space-saving designs. The product paper adds that the connection is backlash-free and maintenance free, and that the selection tool on the RINGFEDER website filters locking assemblies by torque or shaft diameter, with axial displacement and self-centring as further criteria.

Why a keyless locking assembly instead of a keyway

A locking assembly such as the RfN 7110 connects a hub to a shaft by friction rather than by a key. Tightening the locking screws creates radial pressure on the shaft and in the hub bore, and the torque and axial force are carried through that frictional contact. Because no keyway is cut, the shaft and hub keep their full section, the connection has no backlash and there is no fretting at a key under reversing loads. This makes the design attractive for drives that start and stop frequently, change direction or must hold an exact angular position.

Another practical advantage is adjustability. The hub can be positioned axially and angularly on the shaft during assembly and then clamped in place, which helps when timing cams, sprockets, pulleys, gears or levers relative to each other. Because the RfN 7110 locks without axial displacement of the hub, the position set during assembly is kept while the screws are tightened.

Typical applications

The compact, self-centring design suits machines where space is limited and hubs are kept thin, as the tech paper describes. Typical examples include packaging and printing machinery, conveyors, indexing drives, small gearboxes and general machine building where pulleys, sprockets or gears must be fixed securely without a keyway. The stainless steel version mentioned above addresses machinery that is cleaned intensively, such as in food and beverage processing.

Selection considerations

Selection starts with the shaft diameter and the torque and axial force that the connection must carry, including peak and shock loads rather than only nominal values. The hub then has to be checked for its ability to take the hub surface pressure given for the chosen size, which depends on the hub material and its outside diameter. The surface finish and tolerance requirements for shaft and bore listed in the specification table should be built into the machining drawings from the start.

Space for the collar and access for a torque wrench to the locking screws also need to be considered in the layout, particularly on compact machines where neighbouring parts may limit access.

Installation practice in general terms

Clean the shaft and hub bore and follow the RINGFEDER instructions regarding lubrication of contact surfaces and screws. Slide the assembly and hub into position, align them, and tighten the locking screws gradually and evenly in several rounds until the specified tightening torque is reached on every screw. Uneven tightening can affect centring and the achievable torque. For removal, follow the release procedure in the manufacturer instructions.

Use in Oman and GCC plants

In the region, many drives operate in dusty, hot or humid environments, including coastal plants and outdoor conveyors. A keyless connection avoids open keyways where dirt and moisture can collect, but exposed parts of the assembly should still be protected according to the machine design. Where corrosive conditions or frequent washdown are expected, the stainless steel version is worth evaluating. Sending the shaft and hub dimensions, torque, axial load and environment together allows a suitable size to be proposed.

Documents and quotation

The attached PDF is the RINGFEDER RfN 7110 tech paper (06.2025). Drive items are listed under Electric Motors and Gear Units. Send shaft and hub dimensions and the torque for a size proposal.