Note: The dimensions that follow are for an MPP holder. Others may differ slightly.
Originally Posted by lostin_ostin
Overall maximum size of the plate is 4.045"x5.052" - As the plates are only retained at opposing ends, the width is not critical, so anything under 4" will fit. The length should not be less than 4.900", so this needs to be cut fairly accurately or the plate(s) may not be retained securely.
While I have the vernier out, a standard plastic Fidelity DDS is 11mm thick. The wooden MPP holder, 15.75mm - Well within the capabilities of a spring back on modern 5x4 cameras.