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TWINOFFSET LISP: Offset an Object to Both Sides at Once

TWINOFFSET offsets an object to both sides at once. The obvious use is anything with a centreline: roads, walls, ducts, trenches, cable routes. Draw the centre once, offset both faces in a single operation. TWOF is the short alias.

What TwinOffset does

Three options are offered at the distance prompt. Through lets you pick a point instead of typing a distance, and the offset is measured from the object to that point. Erase controls whether the source object is deleted afterwards. Layer controls whether the new objects land on the source object’s layer or on the current one.

The Erase and Layer settings persist for the whole AutoCAD session, so they only need setting once.

How to use it

  1. Load the routine with APPLOAD, or put it on your support file search path.
  2. Type TWINOFFSET or TWOF.
  3. Give the distance, or choose Through and pick a point.
  4. Set Erase and Layer if you need them — they persist afterwards.
  5. Select the objects.

How it works

The distance is held in OFFSETDIST, the same system variable the standard OFFSET command uses. So the two share a setting and neither surprises you after using the other — which is a small thing that stops a routine feeling bolted on.

Offsets are applied through AutoCAD’s own offset engine rather than by computing parallel geometry. That is what makes arcs, splines, ellipses and variable-width polylines all come out correctly, including the cases where a hand-computed parallel would self-intersect on a tight inside curve.

Notes and limits

  • OFFSETDIST is shared with the standard OFFSET command. Setting it here sets it there.
  • Erase and Layer persist for the session, so check them if the results land somewhere unexpected.
  • Through mode measures to your picked point, giving both offsets that distance.
  • One undo group covers the pair.

Download and details

NameTwinOffset — offset an object to both sides at once
DownloadTwinOffset.lsp — 12.4 KB, plain AutoLISP source. Downloads directly; no zip to unpack.
TypeAutoCAD AutoLISP routine
CommandsTWINOFFSET, TWOF
Requiresthe ActiveX layer (loaded automatically by the routine with vl-load-com).
Source size12.4 KB, 304 lines
Error handlingYes — a *error* handler restores every system variable it changed, on cancel as well as on error.
UndoThe whole operation is wrapped in a single undo group, so one U reverses all of it.
CompatibilityAutoCAD (any release with AutoLISP), BricsCAD, ZWCAD, GstarCAD, ProgeCAD and other IntelliCAD-based platforms. AutoCAD LT needs a LISP enabler. No .NET, no ObjectARX, no installer.
AuthorYZ, August 2026
LicenceFree to use, supplied “as is” with no warranty.

References