Speedia centrepin reels are excellent. Only downside is they have a very deep arbour. This two piece plastic insert is designed with a decagonal inside to match the 10 pillars on the ree. And a circular outside, that overall, increases the diameter of the spool by 5mm. There is a loose compression fitting that can be prised apart with a jewellers screwdriver if necessary.
V2----I've edited this to make height 16mm and to cut plastic away where the handles mount on the spool, avoids needing a knife to modify