cross brace K45 and K40

 The middle bars K 45 are suitable for both stretcher frames K 40 and K 45.

from 50 cm length
one slit,  
i.e. a middle bars or a cross: from 2 m length
two slots,
i.e. two middle bars per side or a double double cross:

Depending on the length, the centre pieces either have no slot at all (shorter than 50 cm length), only one slot (from 50 cm length) or 2 slots (from 2m length). Accordingly, further middle pieces should be added so that 2 of them interlock at each slot, forming a cross and thus stabilizing the frame. Matching slots are worked into the wedge frames to anchor the ends of the corresponding centre pieces there.