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

    Default: Supplied by profile                Value: 0-4096

    Packet size, in octets, for transmitted and received data
    packets. The value must be a power of 2 in the range 0 to 4096.
    The value zero indicates that no packet size is included in the
    outgoing call.

    Example:

    set x25 access template TEMPLATE-0 packet size 512