The invention is a method of forming extrudate having substantially uniform thickness. A shim is formed which has a thickness variation of less than or equal to about 0.5 mil (13 microns) total indicated runout. This shim is disposed between a first die portion having a first surface and a second die portion having a second surface. A slot is formed between the first surface and the second surface. The slot has a height dimension substantially the same as the shim thickness. Flowable material is extruded through the slot.