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Well, yes, a third is the..
Well, yes, a third is the twilight zone between pass and failure. It will make it harder to get to interviews. You will need a pretty good reason (not excuse!) for your third.
I studied the things I felt were going to dominate the future. I invested my attention mainly in digital logic and microprocessors, in which I excelled. Things like thermionic valves were antiques even in 1983. I knew I did not wish to work in semiconductor fabrication. However, exams test all aspects of a course and top marks in some sections will not hide low marks in others. I had talent but didn't invest them evenly. Hence my third.
I applied for design work without success. One company said they had could use someone who could explain their products to customers well by phone or in writing. I sent them my final year project report, and they were impressed, and I got in as sales support and technical writer.
Years later I did an MSc without the BSc mistakes, and passed comfortably.
A third is not insurmountable if you know you have some talents and learned where you made mistakes. Take jobs that are not ideal, they are better than no job at all and they pay food and rent while you wait for better opportunities arise. It also shows employers you adapted to survive - a useful ability.
Having said this, degrees are so common these days that you will have to work even harder to shine out in the crowd.
If you got a third through booze, drugs, idleness, and complete lack of aptitude, then a third class degree is not the real problem.