FWIW, I ordered this from Amazon: https://www.amazon.com/gp/product/B00Z40WWQG and a RRS rail from B&H for my Shen Hao 6x17. They both fit. I kinda liked the Amazon one more since it had little rubber feet to compress and keep everything tight.

​

RRS: https://www.bhphotovideo.com/c/product/1301199-REG/really_right_stuff_mpr_1_3_8ths_multi_purpose_rail_6_152mm_with.html

​

They both fit great on my BH-55 ball head with panning.