The rebated grooves where the wedge was inserted were either 'L' shaped, rarely like a 'Y' with one branch missing or even 'U' shaped. Usually the grooves faced the same direction although some examples (see photograph) have the centre groove facing the other direction that were used between fields so that the centre spar would resist being dislodged from the other side. The grooves were cut quite deeply to reduce the chance of the spar becoming dislodged. The grooves were sometimes neatly cut with the skill of a stonemason or rather roughly formed by farm workers, etc.
