"at a spacing" is a correct and usable phrase in written English.
You can use it to refer to the space between two things, such as in the sentence: "The students were seated at a spacing of two meters apart."
IR-maize was planted at a spacing of 90 × 45 cm and 2 seeds per hole.
The planting density was 25 hills m−2, at a spacing of 30 cm × 13.3 cm.
Six girders per span were used at a spacing of 2.4 m (8 ft).
Trickle irrigation laterals were laid out on the soil surface at a spacing of 1.40 m.
In SB3 and SB4 specimens, shear reinforcements were provided at a spacing.
For the 400-mm beam width, two connectors at a spacing of 240 mm were used.
Each plot consisted of five rows with 10 plants per row at a spacing of 16.7 cm × 26.7 cm.
The deck is supported by a grid of longitudinal and crossbeams at a spacing of 1.4 m × 4 m.
Many distributed short lines in Fig. 3 denote the orientations of SHmax at a spacing of 7.5 km.
Twenty-day-old seedlings were transplanted to the experimental plots at a spacing of 50 × 50 cm.
Ten plants at a spacing of 16.5 cm × 26.5 cm were planted in a row and 5 rows of each line were planted.
