It does read Maximinus, not Maximianus and I think this is therefore Maximinus II Daia, as Augustus 310 to 313 AD, not Maximian who was 286 to 310 AD with gaps.
Reverse is Iovi Conservatori Augg NN. The excellent Roman Base Metal coins from the banner advert has it as CRB430 on page 58. Siscia mint - which is modern day Split in Croatia.
Nice coin and well worth your £8. If you are going to collect the odd Roman coin cheaply then the two Rotographic books (one for Silver, one for Base metals) are a great starting place.