An item grouping mechanism may be applied to files or other computer objects to allow the files or objects to be accessed according to the group definition. The method selects an output resolution R, and then determines a number of sub-passes to extract from each block code based on the selected resolution. The low pass section includes a band reject filter formed from slots cut to reject higher frequency signals. The handle portion has a length equal to or larger than half a length of the object along the passage opening when the handle portion is extended in a direction along the passage opening. There is at least one fluid pressure actuated expansion member disposed between and engageable with such first and second member. , the system is thus double-acting.