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. <EOS>