Hi Serge I know Rob once told me the reason for those spacers but for the life of me I can't remember what it was.(knowing him, it was the only available material at the time). I will probably see him within a few days and will ask him then. Pity I didn't download e-mail yesterday because I was as his house yesterday. Regards Dene Collett KR2SRT builder South africa Whisper assembler See: www.whisperaircraft.com mailto: av...@telkomsa.net