An under mattress is provided with springs between the under-mattress cross members and frame as in 2112506. This addition to the patent concerns a method of adjusting the initial compression of individual springs when the under-mattress is already placed on the bedstead. The under-mattress (16) is provided with a number of bolts (20) which clamp a number of thick rubber washers (21) between threaded disc (22) and the upper surface of the frame (16). The cross members (14) are provided with hemi-spherical recesses (26) which fit over the nuts (25) to allow the plastics plate (27) to rest on the disc (22). The compression of the washers can be adjusted by screwing the disc (22) up or down.
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