Don't hammer it. It will likely break. If it just won't slot in, I would file it. Just be careful how much, because they need to be tight fitting.

Also be sure your using the correct side, but I doubt you or anyone could make that mistake.

I always trim the little round bump on the male clip and play connectors. I can usually get them into the slots, but if I don't file or trim them a little, I can never remove them.

Alan

I use a bit of oil around the edges and on the top. They can be rather hard to get apart, usually moreso than connecting them. Especially from rotating servos since you can't really wiggle the connector to help separate them like you can with a lever servo. Gotta watch it when doing so with something like a sonar unit. The wires are so tiny. More than once I've had to solder them back to the little voltage converter. Generally I find grasping something like that with your fingers on one side while pushing with your thumbs on the other side can help on the really stubborn ones.

Thanks everyone,

I ended up spraying the extension cube with some silicon base lubricant and now it can be slide into the hexapod body easily.