Dear Martin,

Sönke Neitzel in his book "Die deutschen Ubootbunker und Bunkerwerften" (Bernard & Graefe Verlag, 1991, ISBN 3-7637-5823-2) writes on page 36:"Der Fang-Rost (Stahlbetonkonstruktion) bestand aus bis zu 3,8m hohen Auflagern, auf die die 1,5m hohen Fang-Rost-Rippen quer dazu aufgelegt wurden. Die Fang-Rost-Rippen waren oben rund bzw. abgeschrägt und durch eine 10mm starke Stahlkappe (es sollte auch Schmelzbasalt verwendet werden, da dieser erfahrungsgemäß am besten widerstand) abgedeckt. Aus Materialmangel ist diese Stahlabdeckung aber selten eingebaut worden. Die Rostrippen wurden in einem Abstand von 30cm zueinander verlegt."

Google translate reads the English text as:"The catch grate (reinforced concrete structure) consisted of up to 3.8m high supports on which the 1.5m high catch grate ribs were placed transversely. The grating ribs were round or slanted at the top and covered by a 10mm thick steel cap (cast basalt should also be used, as experience has shown that this is the best resistance). Due to a lack of material, this steel cover was rarely installed. The grating ribs were laid at a distance of 30 cm from each other."

[www.atlantikwall.co.uk] shows a number of Fangrost-photos (search for the word Fangrost on the site).

The width of the supports and grate-ribs is not listed, but with the above given dimensions of their height, the photos may give you an idea of their width.

We walked once on the roof of the U-shelter at Bordeaux, underneath the Fangrost, but did not take measurements... Sorry.

Best regards,
Walter