At the center of the buttock, 3.5 cun lateral to the posterior midline, on the level of the 4th sacral foramen.
How to locate
First identify the Tuffier's line which connects the highest points of the iliac crest. The spinous process of the 4th lumber vertebra (L4) mostly falls on this line.
Then palpate in an inferior direction, passing L5, and reach the most superior sacral spinous process. Palpate in a lateral direction on the level of the sacral processes for the depression of the sacral foramina.
Tunzhong EX-B is at the same level as the 4th foramina and 3.5 cun lateral to the posterior midline.