Filbert trees need a pollinizer in order to produce nuts. All filbert varieties don’t cross pollinate. There has been a lot of research done at Oregon State University by Rebecca McCluskey and others concerning pollination. There are a number of issues that must line up to make a good match for pollinizing hazelnuts. Timing of the pollen shed to coordinate with the timing of the bloom is vital. Compatible alleles between varieties is the other very important aspect of pollinization.
It is highly recommended that you have at least 3 different pollinizers in an orchard plot to cover the different timing of pollen release. Flowers are open and receptive for a longer period of time than the pollen is released from each variety. The different pollinizers need to cover early, mid and late release, set to the timing of the bloom from your main crop variety. For example, Jefferson is a late bloomer. It needs pollinizers that shed pollen later and much later than an early bloomer like Yamhill.
Here are some papers that will help you with pollinizer selection.