Serially Interlocking [4 piece puzzle]

Just so there is no confusion: a - is red, b - is white, c - is silver, d - is black. The order the connect in is red and black, next silver, lastly white. My puzzle didn't successfully interlock, but that was due to the cubes needing more sanding than I had planned on.
This puzzle took some imagination. I first set to finding the possible ways in which the a and b could interlock, being that these both had two sets of 3 connected cubes. Once I tested out the possibilities, it became clear that there was really only one possibility. Then I had to figure out which sequence to put the pieces together in.
And so it goes from left to right: a (left side facing down, right side facing up), connecting with d (upside down), connecting with c (upside down), and b (looking like an inverted capital J).