Axles designed to move laterally entering a curve in an effort to reduce the flange and rail wear incurred with rigid axles. The design was normally confined to the leading or trailing carrying axles of a locomotive. The idea was first tried successfully by W B Adams of the London & South Western Railway in 1863 and was subsequently taken up by FW Webb and others. The axle could be guided by either curved axleboxes, as in the original Adams design, or by a curved transverse frame as in Webb's design.