Hi gents. Many thanks for the replies. I've had a gander through the Modelwarships.com site and have found some small blocks. At a very rough guess I think that 2 or possibly 3mm blocks may be close enough. I think that the SWL of these booms may have been quite high - I've worked on ships which have had the same type of wooden boom, around the same size, and I think they could take around a ton. Unfortunately I am a radio man and didn't work on deck so I never had to know the SWL of the lifting gear. So anyway, I'm going to order some, they're pretty inexpensive, and will let you know how I get on. Thanks for the tip for the small blocks Ratch, I will try this out for the small blocks dotted around the place. Onwards and upwards!