An assembly (1) is provided comprising a spring break protection mechanism and a spring plug (21, 22, 25;112) for connecting a balancing spring (110) of a sectional door system to the spring break protection mechanism. The mechanism comprises a base plate (2;72) with a circular opening for receiving a balancing axle (100). A ratchet wheel (4;80) is rotatably arranged at a first side of said base plate to cooperate with the balancing axle. A pawl (12;84) is pivotably connected to the base plate. Attached to said pawl is an extension (16) extending from the pawl to beyond a second side of the base plate. The base plate and the spring plug are arranged for bayonet mount interaction wherein if the spring plug is placed against the second side of the base plate and then rotated for bayonet connection, part of the spring plug pushes the extension so as to force the pawl in the first position. If the spring plug is then rotated in an opposite direction, the pawl moves into the second position, to block the ratchet wheel so as to avoid rotation of the balancing axle.