A core die for creating an airfoil includes a first section, a second section mating with the first section, and an insert for creating a slot. The first section and the second section define a body having an outer dimension. The insert is disposed at an angle to the outer dimension. A trip strip includes a first portion disposed in the second section. The first portion is in register with the insert and a thickness is maintained between the first portion and the insert along a length of the insert. The first portion tapers towards the outer dimension and the thickness is filled by the ceramic material between the slot and the first portion.