A two-piece fastening arrangement for joining two structural greenhouse panels. The fastener is capable of connecting a wide range of thicknesses of structural panels. A cap member snaps into a base member and biases the structural panels between the cap and base. The snap engagement is between two sets of cooperative arms extending from each member, one member having hooks which are inserted into recessed areas or notches of the other member. The notched member has a plurality of notches in the arms making the fastener capable of connecting a wide range of different width panels. The cap member has a crescent shape to bias the structural panel and improve the sealing of the joint. With the crescent shape and size of the notches, different thicknesses of panels can be connected to each other with a uniform fastener.