Step 1:

Sketch the design to understand the concept

Step 2:

Draw the first part on the solidworks. Which is made of a triangle and two circles where the first circle is related to the two sides of the rectangle as tangent and the second circle is inside the first circle and the triangle. After adjusting the desing and the dimensions according to the dimensions of your soldering wire tube.

Step 3:

Test your desing dimensions by printing one part and make sure that your dimensions fit.

Step 4:

Start adding the interlocks to the side and the base part. And the interlocking dimensions are adjustable according to your prefernces. However, make sure that the interlocks in both parts are fitted together. My dimensions are found in the following images

Step 5:

Bring all the parts together and construct the final shape.