As we known ,knit line caused by plastic material flow confluence. also named "fusion line". it usually will be very obviously when the material flow fluidity weak. for example.when mould tempreature is not enough high or material properity is poor fluidity. PP,PA will be better,but like PC or GF reinforced material will often appear clearas below photo. As experience,knit line cant be avoided completely but sometimes can improve much through several thoughts as below. 1) to enhance mould work tempreature. 2) make part color lighter,usually lighter color will be much better to hide the knit line. 3) to make deeper texture to cover it . 4) Moving injection gates to make material flow directions change,then to make confluence to the other unimportant location. 5) certainly ,most of time,we are troubled by the knit lines around the holes which usually important appearance.i advise to cover the holes and open it after moulding.then can get perfect outside .