I'd prefer steel or hardened aluminum ...only because they would be less likely to compress with installation tq . and forces applied during driving over time.
Poly may work fine ??? I've just never had a poly wheel spacer .
Imo Bora wheel spacers are worth the added $$ , and certinly do get hub & wheel centric !
Do not get the (Chinese or the likes ) made one size fits all , as that is where the bad rep for wheel spacers come from [emoji106]
I've had steel and aluminum without issues with proper installation and torque verifications .
If you go less than 1.75" spacer thickness , just know you will likely need to either replace your OEM studs to a shorter one or trim your OEMstuds ...depending on your wheel selection .
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