As well as giving more exposures per roll of film the smaller format (up to 4 x 4 cm) allowed colour transparencies to be used with most projectors taking 35 mm slides.

This was a popular device, remaining on sale until the 1950s when some of the fittings were incorporated in the camera, the Rolleikin (known as the model II) then no longer needed the replacement back.

There were three versions of the Rolleikin I:

• Type 1. The earliest version did not have a rewind facility, the film was wound into a take-up cassette, a film cutting knife was used to separate the film from the feed cassette. For the Rolleiflex the outfit consisted of a camera back, film gate, view-finder mask, spool (cassette) holder for the take-up chamber and an empty take-up spool. The feed spool fitted into the chamber under the existing retaining spring. For the Rolleicord an extra spool holder and spool were supplied for the feed chamber.
• Type 2. The next version had a rewind facility and did not have the cutting knife. This model fitted the Rolleiflex Automat and Rolleicord II. The outfit consisted of a camera back, film gate, view-finder mask, spring-loaded release knob to fit the take-up chamber, rewind knob to fit the feed chamber, spool holder for the feed chamber and a take up spindle.
• Type 3. The last version was similar to the type 2 except that the feed spool was not held in a holder, a short spigot attached to the inside of the rewind knob and held the spool, a spacing piece fitted at the other end of the spool.

The Rolleikin II replaced the model I, early models were supplied in a metal box and had only a single 'extension piece', later it came in a leather case and had two 'extension pieces'.

The parts included in the outfit were:

• Direct-vision view-finder mask, clips to the folding hood of the camera.
• Focusing screen mask.
• Lens hood mask.
• Screw head cover, leather piece to place on Release knob.
• Retaining screws, to fit Release knob.
• Release knob with exposure counter.
• Extension spindle for rewind knob, two were supplied on later sets to fit different camera variations.
• Intermediate knob, fits to one side of the 35 mm cassette.
• Film guide plane.
• Take-up spool.