Si tratta di un termine (muntin)usato principalmente negli USA.
(Ed anche di un tipo di finestre usato principalmente negli USA).

Ho trovato parecchi siti che ne parlano, alcuni con foto.

Io lo tradurrei come: "sistema per finestre con montanti (reggivetro)".

MUNTIN (mun tn)
In traditional "grid" wood windows, the bar that holds the separate window panes within a sash. See GRIDS.
http://www.certainteed.com/cwindows/cwct00081g.html


A: A "lite" is a pane of glass. A sash (or door) with six lites is a sash that is divided into six individual panes of glass, with each pane separated by a muntin bar (the dividing strips between the panes of glass.) There are several techniques used to create divided lites:

http://www.buildersexpress.com/glossary.asp?browse=1&camefro...

Muntin - vertical central part of the door between panels.
http://www.trp.dundee.ac.uk/research/glossary/door.html

Muntin: A main vertical framing member of a stile, specifically the central upright connecting the top and bottom rails of a frame.
Stile: A subsidiary vertical framing member of a muntin, or the outermost vertical section of a panelled construction.
Rail: A horizontal framing member in joinery, such as a seat-rail, table carcase, chair frame, back-rail etc., or as found in a door.
http://www.brownowl.com/gloss_m.html

Muntin: A muntin is the grid work that separates the panes of glass in a sash.
http://www.bi-glass.com/glossary_of_terms.htm

Lo trovi anche nei glossari.