I needed to support lightweight trellis a little way from the back side of traditional featherboard fencing, with no effect on the fencing.

Design and construction

The fencing panels had three horizontal arris rails of the traditional size (that is, cut from 3 in or 75 mm square posts). I used spare softwood sticks of cross-section 43 mm by 20 mm to create mounts that would mate with the rails. As it happened, I already had many scrap triangular pieces. Each mount would support one corner of the trellis.

The triangular pieces were attached to the rectangular ones with exterior wood glue. The assembled mounts were protected from the weather by staining.

The mounts were attached to the arris rails with two 4 mm by 50 mm wood screws. 4 mm guide holes for those screws were drilled into the triangular pieces, once they were attached to the rectangular ones.

I could not find a commercially-available product that replicated the function of the mounts.

Result

The result was as I intended. Given their purpose, including that they would largely be hidden, I did not need to refine the construction of the mounts.