Trend LB/JIG Letterbox JigEnables the cutting out of letterbox openings to be carried out quickly and accurately. The size-adjusting jig ensures that template openings are always cut exactly square. Made from cast aluminium and machined to a high standard. Simple to set up and use. Requires 1/2 inch diameter x 50mm cut lng. cutter. Unibase may be required for certain makes and models of router.Specification-Max aperture.=310 mm x 82 mmMin aperture.=210 mm x 46 mm