Tension-adjusting device for a chain in chain saw

A tension-adjusting device for a chain in a chain saw, comprising an adjusting assembly, a fixing base, a brake disk, a position piece and a fixing piece, wherein the adjusting assembly, the brake disk, the position piece and the fixing piece are locked together on the fixing base by a bolt, the adjusting assembly is located at an outside end of the fixing base while the brake disk, the position piece and the fixing piece are located at an inside end of the fixing base, the adjusting assembly is connected to the brake disk, and the brake disk is engaged with the position piece via spiral guide rails on the brake disk and projections on the position piece whereby each spiral guide rail in its width direction can be properly fitted into the space between two adjacent projections such that the spiral guide rail can smoothly pass through the space between the two adjacent projections on the position piece;

• wherein the adjusting assembly comprises a knob, a nut, a fixing member and a adjusting ring, one end of the knob is formed into a hollow polyhedron, one end of the fixing member is also formed into a hollow polyhedron, the adjusting ring is provided with a hollow disk, one end of the hollow disk is formed into a polygonal recess for receiving the hollow polyhedron of the knob whereby the nut is combined into the hollow polyhedron of the fixing member, the hollow polyhedron of the fixing member is combined into the hollow polyhedron of the knob, the hollow polyhedron of the knob is combined into the polygonal recess of the adjusting ring, and the bolt penetrates through the fixing piece, the position piece, the brake disk and the fixing member to be screwed and fixed into the nut.