carbitool/smartbit

Hi there,
I am just about to start laying merbau decking with 10g x 50mm s/steel deck screws from home trade products & would like your thoughts on my question. I have seen very old posts on which is better for pre drilling/countersinking, carbitool v smartbit. I have not been able to see a smartbit in the flesh but have seen the carbitool which came with either a 3.2mm or 4mm bit. I noticed that the drill bit was 70mm long & then another 10mm for the countersink stage. With these dimensions in mind & allowing for the 20mm thickness of the merbau is it ok to drill 60mm into the treated pine joists or will it weaken the strength of the screws. I have also noticed on previous posts that you should pre drill using 3.5mm, is it possibe with the carbitool to remove the 3.2mm bit & replace with 3.5mm?

Cheers
Welshy :U


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