"The castor configuration is two swivel castors, one braked and one brake /directional lock castor."
www.autwheelsandcastors.com/ series_hbed_page157to158.pdf

I also found "function to lock the direction":

German version: "...als totalfeststellbare Lenkrolle, die zusätzlich richtungsfeststellbar ist."
http://de.red-dot.org/47 M533906ee62b.html

English version: "...as a totally lockable castor with an additional function to lock the direction"
http://en.red-dot.org/47 M533906ee62b.html


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Note added at 25 mins (2005-06-09 18:03:47 GMT)
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Some more search results:

... movement of the caster wheel fork, ie anti-swivel or directional lock mechanisms. ... Inventor: Hall; 5377372; Hospital bed castor control mechanism ...
www.patentstorm.us/patents/6321878.html - 85k - Cached - Similar pages


Products Report-0Castor type available -Swivel -Fixed -Directional lock-wheel free/total lock Mounting Fittings option ... “RUBY” Style Central Locking Hospital Bed Castors ...
www.fcc-fmh.com/Products Report/ Products%20Report-2.htm

... 3/ Fit Directional Lock castor into the right hand front (leading end) of the bed (ensuring that the arrow on cap is pointing to the front (leading end). ...
www.fallshaw.com.au/central_braking/ images/cl_full_inst.pdf

... Hospital Bed Castors. Precision ball bearing swivel yoke, Total Lock / Directional Lock central locking system Types: Total Lock / Directional Lock castor; Total ...
www.castorwheel.com/catis.htm