-SG- The standard 1929 product range was fitted with circular knee grips on either side of the tank. These were secured onto short protruding 5/16 x 26TPI studs on the tank sides. Very good replicas have been available for several years from Hunters in the UK - contact email@example.com or by post Jeff Hunter Eng. 35 Sandgate Road, Hall Green, Birmingham B28 0UN. Cost is £36/pair plus £5 post and packing and I understand payment can be by cheque or PayPal (PayPal fee exra £1.53).
Worth mentioning that Hunters also make replica George Dance knee grips as fitted to production CS1s and ES2s and earlier machines built to racing spec. Price of them is £62 pair plus £6 post/packing by cheque or PayPal (PayPal fee extra £2.34).