A drive gear for use with an electrical generator comprising: a gear hub having a ledge portion with a plurality of gear teeth at an outer periphery and centered about a central axis, and said gear hub having a mount extending axially away from said ledge , a first distance (d1) being defined between axial ends of said gear teeth , a second distance (d2) defined between ends of said gear hub, wherein the axial ends of said gear teeth include a remote end , remote from the ledge , characterised in that : a ratio of said first distance (d1) to said second distance (d2) is between 0.520 and 0.544; and in that : said gear teeth have a flat radially outer end and curved sides , with there being four roll angles (V, X, Y, Z) on each of said sides , with a first roll angle (V) extending for 6.70° to 8.70°, a second roll angle (X) extending for 11.10° to 13.1°, a third roll angle (Y) extending for 24.4° to 26.4°, and a fourth roll angle (Z) extending for 28.9° to 30.9°, wherein said drive gear has an internal bore, with a threaded radially inner bore portion extending from an axial location of said remote end of said teeth , and there being a radially outer bore portion at said mount, wherein there is a radially outwardly extending ditch located between said threaded radially inner bore portion and said radially outer bore portion . a gear hub having a ledge portion with a plurality of gear teeth at an outer periphery and centered about a central axis, and said gear hub having a mount extending axially away from said ledge , a first distance (d1) being defined between axial ends of said gear teeth , a second distance (d2) defined between ends of said gear hub, wherein the axial ends of said gear teeth include a remote end , remote from the ledge , characterised in that : a ratio of said first distance (d1) to said second distance (d2) is between 0.520 and 0.544; and in that : said gear teeth have a flat radially outer end and curved sides , with there being four roll angles (V, X, Y, Z) on each of said sides , with a first roll angle (V) extending for 6.70° to 8.70°, a second roll angle (X) extending for 11.10° to 13.1°, a third roll angle (Y) extending for 24.4° to 26.4°, and a fourth roll angle (Z) extending for 28.9° to 30.9°, wherein said drive gear has an internal bore, with a threaded radially inner bore portion extending from an axial location of said remote end of said teeth , and there being a radially outer bore portion at said mount, wherein there is a radially outwardly extending ditch located between said threaded radially inner bore portion and said radially outer bore portion . said gear teeth have a flat radially outer end and curved sides , with there being four roll angles (V, X, Y, Z) on each of said sides , with a first roll angle (V) extending for 6.70° to 8.70°, a second roll angle (X) extending for 11.10° to 13.1°, a third roll angle (Y) extending for 24.4° to 26.4°, and a fourth roll angle (Z) extending for 28.9° to 30.9°, wherein said drive gear has an internal bore, with a threaded radially inner bore portion extending from an axial location of said remote end of said teeth , and there being a radially outer bore portion at said mount, wherein there is a radially outwardly extending ditch located between said threaded radially inner bore portion and said radially outer bore portion . <EOS>