The phrase "a certain shape or" is correct and usable in written English.
It can be used when describing an object or concept that has a specific but unspecified shape or form.
Example: "The sculpture was designed to evoke a certain shape or form that would resonate with the viewer's emotions."
Alternatives: "a particular shape or" or "an unspecified shape or".
Collectors buy smaller rocks; sometimes they've been carved into a certain shape, or they may contain a mineral pattern with an uncannily familiar form.
The trio speculated that these refinements contain information that our eyes recognize as the style of the artist: how often the artist employs lines of a certain shape or degree of tilt.
"To think that because you're of a certain shape, or weight, that people are not going to be attracted to you is just not true".
So, too, we were before we were taught to believe anything, learned anything, were in any kind of relationship to other things, before our body took a certain shape, or we experienced any particular history.
This nonlinear approach resulted in smooth lines following the data without adjusting to a certain shape or predefined statistical model.
A glass which is a certain shape or has been frosted in a particular way can make your drink instantly recognizable.
We explored the optimum parameters for each neuron as follows: We first tested color selectivity using a certain shape (usually circle or the optimal shape for the neuron tested immediately before).
Even if one grants atomic sentences containing non-denoting singular terms and that some attributions of vague predicates are neither true nor false, it nevertheless seems natural not to preclude that compound sentences of a certain shape containing non-denoting terms or vague predications are either true or false, e.g., sentences of the form 'If A, then A'.
But if you ask a very specific question, like how dangerous are titanium nanoparticles of a certain size or a certain shape and what are we going to do about it, then you've got something that you can begin to apply scientific principles to".
That is, whether or not a certain shape is handed depends only on the distances between its constituent particles.
Then again, the commodity in question is not the typical stuff of e-commerce transactions, like a plane ticket from Cincinnati to Nashville next Thursday or a vintage Barbie doll or 20,000 widgets of a certain shape.
