5 predated the 5a, and was made about 1926 - 28, it was the sight that was responsible for the breakup of Alfred G. Parker and his son Alfred J. Parker, who left the company and started his own business.
A.G PARKER- Bisley works, became Parker Hale in 1930, after settling the dispute over sight copywrite with A.J. Parker, the original designer.
The Hale connection was an inter marriage one, but the Hales worked their way into management positions that eventually saw the breakup of the original company.........quite a convoluted story, but interesting enough for the serious sight collector.