Library /sys$common/syshlp/ncphelp.hlb CLEAR, LINE, MAXIMUM_BLOCK  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Applies only to X.25 lines.  Resets the MAXIMUM BLOCK parameter to
 the default value for the specified line or all known lines  in the
 volatile database, or removes the MAXIMUM BLOCK value from  the
 permanent database.