Prop

A prop which includes a first tubular member with a closed first end and a flared mouth at an opposed, second end, a second tubular member which extends into the first tubular member, through the flared mouth, which has one end inside the first tubular member and an opposed end which is sealed, a one-way filler valve connected to one of the tubular members through which a pressurised fluid can be introduced, at least, into an interior of the first tubular member, a seal which acts between the tubular members and which permits outward telescopic movement of the second tubular member relative to the first tubular member as an interior of, at least, the first tubular member is pressurised, a component which is located in the flared mouth around the second tubular member and which is frictionally engaged with, at least, an outer surface of the second tubular member, and a pressure relief valve which allows fluid to escape at least from an interior of the first tubular member, when the pressure of the fluid reaches a predetermined value, as the second tubular member is telescopically moved into the first tubular member.