to fit over the pins 34 as previously described and the outer ends of the transverse members 30 have an internally threaded bore member 38 rigidly secured thereto threadedly connected within each member 38 is an extension shaft 40 which has a head 42 for receiving a tool to permit turning of the shaft 40 for extending and retracting the length of the transverse member 30 the end of the shaft 40 has a projection 42 thereon which can penetrate the hole 48 in the inverted saddle member 50 which is retained on the arch member 6 by means of the fastening element 52 thus to erect the basic shelter module 12 the inverted saddle member 50 can be secured onto the arch member 26 at its apex and the transverse member 30 can be positioned between the hub 28 and the aperture 48 located at the apex of the arch member 26 and extended so as to provide with base members 20 and arch members 26 a frame on which the flexible fabric material 54 can be fitted the flexible fabric cover 54 that forms the substrate of the wall structure 56 can be any suitable tent material and in the illustrated embodiment of the invention is an 8.