Mechanism for setting a dose on a drug delivery device comprising a shaft with a helical thread engaged with a nut member, wherein the helical thread comprises a first, second and third pitch
596701 A dose setting mechanism for a drug delivery device, such as a pen type drug delivery device, with a cartridge of medication, wherein the dose setting mechanism is operable to select a dose of medication which shall be administered out of said cartridge is disclosed. The dose setting mechanism comprises a shaft (30), a helical groove (32), and a nut member. The nut member is disposed on the helical groove of the shaft. The helical groove has a first pitch provided along a first portion (34) of the shaft, a second pitch provided along a second portion (36) of the shaft, and a third pitch provided along a third portion (35) of the shaft, wherein the second portion is provided at the end of the first portion and the third portion is provided at the end of the second portion. The second pitch is greater than the first pitch and the first pitch is generally equal to the third pitch. The second pitch acts as a means for preventing a user of the dose setting mechanism from setting a dose of the medication that is greater than any remaining medication in the cartridge. During dose setting of the drug delivery device, the shaft is rotated relative to the nut member while the nut member traverses in longitudinal direction along the helical groove from a first end of the shaft towards a second end of the shaft.
