YDC B series lightened core-through jack is a new product researched and developed by our corporation based on the original YDC series jack. It selects new-style sealing material and intension of high pressure automatic-reinforcement oil cylinder. It improves the structural size of the jack and meanwhile the length and external diameter is minimized, thus the length of reserved strands is reduced and is a jack highly commonly used and wildly in various previous-stressing and post-tensioning prestressing constructions.