An actuator assembly, comprising: a housing defining a housing bore that extends from a first housing end towards a second housing end, along a first axis, the housing defining a flared portion that extends from the first housing end; a piston rod at least partially slidably disposed within the housing bore, the piston rod defining a piston bore that extends from a first piston rod end towards a second piston rod end; and a lost motion device, comprising: a slider having a head that is disposed within the housing bore and a neck extending from the head that extends into the piston bore; wherein the head is provided with a first sealing projection and a second sealing projection that engage the housing bore; and a hydraulic sealing groove defined between the first sealing projection and the second sealing projection; the head is slidably engaged with the housing bore; the head having a head diameter and the neck has a neck diameter that is less than the head diameter, characterised in that: the neck defines an elongated opening that is arranged to receive a pin that extends through the first piston rod end to movably connect the slider to the piston rod, the pin enabling the slider to move relative to the piston rod at least until the pin engages an end of the elongate opening; and the head extending between a first head end and a second head end along the first axis, the head defining a first bearing ring groove that is disposed proximate the first head end and a second bearing groove that is disposed proximate the second head end, each of the first bearing ring groove and the second bearing ring groove being arranged to receive a seal or a bearing ring. a housing defining a housing bore that extends from a first housing end towards a second housing end, along a first axis, the housing defining a flared portion that extends from the first housing end; a piston rod at least partially slidably disposed within the housing bore, the piston rod defining a piston bore that extends from a first piston rod end towards a second piston rod end; and a lost motion device, comprising: a slider having a head that is disposed within the housing bore and a neck extending from the head that extends into the piston bore; wherein the head is provided with a first sealing projection and a second sealing projection that engage the housing bore; and a slider having a head that is disposed within the housing bore and a neck extending from the head that extends into the piston bore; wherein the head is provided with a first sealing projection and a second sealing projection that engage the housing bore; and a hydraulic sealing groove defined between the first sealing projection and the second sealing projection; the head is slidably engaged with the housing bore; the neck defines an elongated opening that is arranged to receive a pin that extends through the first piston rod end to movably connect the slider to the piston rod, the pin enabling the slider to move relative to the piston rod at least until the pin engages an end of the elongate opening; and the head extending between a first head end and a second head end along the first axis, the head defining a first bearing ring groove that is disposed proximate the first head end and a second bearing groove that is disposed proximate the second head end, each of the first bearing ring groove and the second bearing ring groove being arranged to receive a seal or a bearing ring.