A trapezoidal concrete wireless mast stay wire anchor 17C for mast 17, for the 1923 antenna extension array, which used 400’ steel lattice masts to support the inverted-L antenna. Three such anchors per mast were used for single-height staying. Each anchor featured an iron attachment point for turnbuckle tensioners and two iron loops, for temporary mast guying during erection, either side. It measures 3.5m long by 2.5m wide and up to 0.3m high.

Source: Rowlands, J., Marconi's Carnarvon Station 1912-1939: a journey into early commercial wireless in north Wales' Second Edition, 2023.