Convenience sampling (an instance of non-probabilistic sampling). You might call it multi-stage convenience sampling.
If you used convenience sampling to choose the experimental units in each industry, your sampling scheme is convenience sampling. Even if you chose the manufacturing sector randomly, it remains convenience sampling. Even if you chose the industries randomly it remains convenience sampling. If the latter two are also convenience sampled it naturally stays convenience sampled (here you might say it is a combination of convenience and purposive sampling).
Bottom line is you can't get the convenience out of your sample.