Help identifying inverted wedge with studs on the slope I have found these bricks (images below), which have "Lego" branding, but there is no model numbers on it.

The white brick has "4" and "A" on the back, and the red has "6" and "A".

I've searched BrickLink for ages to no avail.
It's an old piece from 1969 - 1982, typically used for train cars or trucks with buckets that could be tipped to dump their contents.

3145 Vehicle, Tipper End Flat with Pins



There's also a newer variant from 1996 - 2016 without the pins and hole.

30022 Vehicle, Tipper End Flat without Pins