If it had not caused so much interest, I would not have returned to the subject of Thomas v Arab valve-gear (April issue, pp 423/4). Confusion may have been caused by a slip which caused me to say the valve stem protruded through slots in the rocker extremities, when through the spring extremities was intended. Also, in saying the Arab engine had normal rockers, one for each valve, this was not meant to imply that Thomas used any other arrangement. Both engines had two rockers per cylinder but Railton, in his Arab engine-formation, used less elaborate rockers, not of girder-type, off-set to enable separate cams for inlet and exhaust valve to be used, and with pads in place of the roller cam-followers favoured by Parry Thomas. While on this subject, the Maudslay engine referred to as another engine with eccentric-oh-camshaft drive also had this at the back of the cylinder block and when I said I could not think of another car engine with this kind of silent camshaft drive I was back in the 1920s. In fact, in 1958 NSU used such a drive on the Prinz. W.B.