Library /sys$common/syshlp/nclhelp.hlb set, x25_access, template, window_size  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Default: Supplied by profile                     Value: 0-127

    Window size for transmitted and received data packets. A zero
    value indicates that no window size is included in the outgoing
    call.

    Example:

    set x25 access template TEMPLATE-0 window size 7