Experiments are designed to explore the maximum static friction F on a dragged probing rod in a granular pile contained in a cylindrical vessel. The results show that F decreases with the radius R of the cylindrical vessel increasing when R is smaller than 0.040 m, and F scarcely changes with R for R >0.045 m. Curve fitting shows that F is as a function of h (the height of the granular pile), namely F=A［h+B(e-h/B-1)］, here the parameter A relates to the shape of probing rod and the flow rate of injecting granules into the cylindrical vessel, and parameter B depends on the flow rate of injecting granules into the cylindrical vessel.