I created a custom family of Y-Strainer it works good but the Strainer part size starting from 100mm to 350mm needs a little bit of offset and I dont know how to work it out using a paramter with reference line here I attached a file.
Create a reference line that begins at the intersection of the horizontal part and the diagonal. The start of the line should be locked to the intersection. Control the length of that line with a parameter. Then, align and lock the length of the profile of the revolve that creates the strainer, to that length parameter. (By the way, I would do that outside of the sketch. I've noticed that all your references and dimensions are inside the sketches of the parts).