dropped down a downhole string not shown and the circulating sub 10 to at least partially block the inner passage or throughbore 52 fig1 of the circulating sub 10 thereby operating the circulating sub 10 to an open configuration as shown for example in fig2 b and 2 c as will be discussed in detail subsequently not shown in the fig5 view are slots 28 seen in fig1 of the seat member 26 which allow downhole fluid to partially flow past the seat member 26 through the inner body member 14 even when a ball 54 has landed on the seat member 26 the seat member portion comprises a circumferential or transverse groove 68 around an outer surface of the inner body member 14 in which a seal such as an u2018 o u2019 ring seal 35 can be mounted to prevent downhole fluid from flowing past the outer side of the seat member 26 at a lower end of the seat member 26 there is a first shoulder 70 and below this shoulder 40 the outer diameter of the inner body member 14 is slightly less than the outer diameter at the seat member portion 26 in this reduced diameter part the inner body member 14 comprises one or more holes or slots 22 which are evenly distributed around the circumference of the inner body member 14 and are elongated along a longitudinal axis of the inner body member 14 the.