Freight is major source of income of the State Railway of Thailand (SRT); which had revenues of one billion baht a year. The development of freight by rail system to be fart punctual and safe is important. Knuckle pin serves tension and shear stress in pulling Rolling Stock. Strength testing of Knuckle pin must be done by technical and engineering knowledge. SRT has 6000 Rolling Stocks; that means 6000 Knuckle Pin has been used and it is likely to increase due to the construction of the Double Track Project and the purchase of new Rolling Stocks. The efficient Knuckle Pin prolongs lifespan and SRT would have benefit on saving cost of maintenance and increase safety in the transportation of goods. This research is aimed at creating the understanding about the quality of the Knuckle Pin modeled Nat Mall. The pin would be test by Standard Test Methods for Tension Testing of Metallic Materialsand the Standard Test Method for Analysis of Carbon and Low-Alloy Steel by Spark Atomic Emission Spectrometry and Hardness Testing Machine and Microstructureto determine the cause of pin’s damage. This study will contribute the standardization of the quality of the Knuckle Pin which is used in Rolling Stocks of SRT.