Supplied as a set of 4 the arch ground sockets come with a driving cap which makes installation easier. Once installed the arch uprights can then slide into the ground sockets for greater stability.
The ground anchor sockets are not tough enough for very heavy clay soil with stones and roots in it. Most of them went in OK but a couple bent in at the top under the force of the hammer blows, trapping the driving cap in the top of the spike. The welds between the flat plate and round part of the driving cap then failed and the round part dropped inside the ground socket. I had to remove the ground socket and grind off the bent-over top lip and start again. Unfortunately you can't just move over a couple of inches if you hit hard ground, they anchor has to be in the right place for the legs of the pergola. In the end I had to use an auger to drill a hole, put the ground anchor in and backfill.
Well made arch. Went in easily - we paid attention to the other reviews and made sure everything was square.
Its ok for getting an arch installed but you need to be careful lining up and checking for level.I was a little concerned that the tops which took the pounding with the special cap began to buckle and endangered the actual entry for the arch to sit in.