Here we have F-scale poling pockets in the style of the Climax A Locomotive. These are intended to be printed in detail plastic or stainless steel. The design and mounting arrangement are described in Ed Hume's book,
A Climax Class A Live Steam Locomotive, (ISBN 978154545404898). The holes are sized for two #0-80 and one #3-48 hex head screws. The #0-80 screws are separated vertically by 0.406 and the holes are separated horizontally by 0.422. The outside of the plate is 0.688" x 0.563". There is more information on the book and the author at
http://Model-Shop.net. The book shows photos of the pockets being made by silver soldering lathe-turned pieces into CNC-shaped plates. Purchasing printed pockets is a convenient alternative.