1. H.S. Yan, The beauty of ancient chinese locks, ancient chinese machinery cultural foundation, Tainan, Taiwan, 2004.
2. China at work: an illustrated record of the primitive industries of China's masses;Hommel,1937
3. On the spring configurations of ancient chinese locks;Yan,2000
4. Design consideration of ancient chinese padlocks with spring mechanisms;Yan;Mech. Mach. Theory,2004