The phrase "are very stringent but" is correct and usable in written English.
It can be used when discussing rules, regulations, or standards that are strict, followed by a contrasting point or exception.
Example: "The regulations are very stringent but allow for some flexibility in certain circumstances."
Alternatives: "are quite strict yet" or "are highly rigorous but".
In the U.S., the rules will be very stringent, but that's because of the bill Congress passed on Friday".
The proposed index has been shown to be more rigorous because it uses quality thresholds from the Quebec IQBP index (reputed to be very stringent), but yet it conserves the expert knowledge embodied in the Moroccan IMBP index.
Our approach was very stringent but probably missed a lot of information due to the Monte-Carlo simulation, which likely explained why we did not replicate results from "classic" GWAS.
Electrostatic force can be calculated based on the principle of energy dissipation, without any approximate treatment used, but there are very stringent requirements for experimental conditions, and ultrahigh vacuum and ultrahigh pulse environments are required to ensure a very high signal-to-noise ratio.
Often there are income requirements that are very stringent so if a person makes a few dollars more than the maximum, but not enough to afford the medication, they are stuck in a gap.
"If it is to be a sail training vessel, controls are very stringent.
The number of requirements (some of which are very stringent) results in a very low probability that they will all be met.
The reason is that the government's targets are very stringent, and everyone in the hospital is working towards meeting them.
China is now a bigger carbon polluter than the United States, so don't expect a tax or cap-and-trade rules to solve global warming, even if American measures are very stringent — and they probably won't be, because higher home heating bills are not a vote winner.
And there are very stringent requirements around managing ERISA money.
