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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Imperial or Metric - Pros and Cons
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<blockquote data-quote="Mike 40M" data-source="post: 141939" data-attributes="member: 3599"><p>Steve, you must have a very worn 13mm spanner if it fits on a 1/4W which nominally is 13.34mm.</p><p>Though I live in a metric country, I've noticed some advantages with UN or BS threads.</p><p>You don't need to use the vernier caliper to determine spanner size. You immediately can see the difference between 1/4W and 5/16W. In the metric world, you never know if it is 12 or 13. 16 or 17, 18 or 19 as they have changed standard a couple of times.</p><p>Though Norton and BSA in their infinite wisdom partly changed from Cycle threads to UN threads in the late sixties. The shield under the engine on my Victor Specials is fastened with two UNF screws and one Cycle thread bolt. Luckily our Vincents are not affected.</p><p>Another drawback with metric threads is that normal metric is rather coarse. Fine threads are difficult to find and varies a lot in pitch. Both UN and British Standard are defined in both coarse and fine.</p><p>I actually fitted Cycle thread screws on my sons Honda CBR600RR for a phone holder. It had two unthreaded holes in the fork top crown which had right diameter for tapping 5/16 BSC.</p><p>One thing I use metric sockets for on British bikes is Monobloc and Concentric main jets, where AMAL recommend 8mm.</p></blockquote><p></p>
[QUOTE="Mike 40M, post: 141939, member: 3599"] Steve, you must have a very worn 13mm spanner if it fits on a 1/4W which nominally is 13.34mm. Though I live in a metric country, I've noticed some advantages with UN or BS threads. You don't need to use the vernier caliper to determine spanner size. You immediately can see the difference between 1/4W and 5/16W. In the metric world, you never know if it is 12 or 13. 16 or 17, 18 or 19 as they have changed standard a couple of times. Though Norton and BSA in their infinite wisdom partly changed from Cycle threads to UN threads in the late sixties. The shield under the engine on my Victor Specials is fastened with two UNF screws and one Cycle thread bolt. Luckily our Vincents are not affected. Another drawback with metric threads is that normal metric is rather coarse. Fine threads are difficult to find and varies a lot in pitch. Both UN and British Standard are defined in both coarse and fine. I actually fitted Cycle thread screws on my sons Honda CBR600RR for a phone holder. It had two unthreaded holes in the fork top crown which had right diameter for tapping 5/16 BSC. One thing I use metric sockets for on British bikes is Monobloc and Concentric main jets, where AMAL recommend 8mm. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Imperial or Metric - Pros and Cons
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