This is the product that I am referring to:
https://www.ji-horng.com/show/plastic-buckle-what-is-side-release-buckle.htm
What do you call the head/male/protruding piece. What do you call the tail/female/inverted piece?
This is the product that I am referring to:
https://www.ji-horng.com/show/plastic-buckle-what-is-side-release-buckle.htm
What do you call the head/male/protruding piece. What do you call the tail/female/inverted piece?
The main part, the female one often with the release button, is called the 'buckle'. This is a common word and what people usually will call this thing.
The smaller flat part that sticks in is called the 'tongue' or 'latch plate'. These are somewhat technical terms and native speakers will understand them but most likely won't produce these terms easily.
It usually comes out as 'stick it into the buckle' (where 'it' is understood by pragmatics to be the male part). Or simply 'buckle your seatbelt' with no mention of the parts. If a non-technical native speaker needs to refer to the male part, it would most likely come out as 'the flat part' (and the female part very naturally as 'buckle').
The Wikipedia article on seat belts mentions this terminology but, as is usual with encyclopedia articles, doesn't use language the way non-technical people do.
You could call them plug and socket if you want to avoid gender-based terms.
Merriam-Webster has
plug
any of various devices resembling or functioning like a plug: such as
a : a male fitting for making an electrical connection to a live circuit by insertion in a receptacle (such as an outlet)
b : a device for connecting electric wires to a jack
and
socket
: an opening or hollow that forms a holder for something
According to Wikipedia, the names are male buckle member and female buckle member, so pretty close to what you called them:
Side release buckle
A conventional snap-fit buckle that is formed by a "male" buckle member—the hook end—and a "female" buckle member—the insertion end. The male buckle member consists of a center rod and two spring prongs equally spaced from the center rod. The two spring arms each have a retaining block that terminates at the front end. The female buckle member has a front open side and two side holes which hold and secure the two spring arms of the male buckle member.[21] This sort of buckle may be found connecting many strapped items such as pet harnesses, safety harnesses, personal flotation jackets, fanny packs and other bags, belts, gun slings, and boots. It is also known as the "parachute buckle". They are often used in conjunction with tri-glide slides.
UPDATE 8/26/22:
If you are unsatisfied with the above, since what you describe is very much like what fastens a seatbelt, which has a male side that is called a "latch" and a female side that is called a "buckle" (i.e., the latch slides into the buckle until it latches), I'd imagine you could get away with using those terms instead.