This item is for the disctinctive round head 'captive notch' type engine bolts and 5/16 x 25tpi nut combination, as fitted to the top clamp of early type douglas 2 3/4hp girder forks (approx 1912-18). These bolts are CNC'd in stainless steel with correct threads and have a captive silver steel pin fitted in each bolt.
the Item listing is for one bolt (with silver steel pin fitted), one nut and one washer - all in stainless steel.
As with the engine bolts we also manufacture (Item 0976) - these round headed bolts were of the type originally fitted to the early type of forks on Douglas models between (approximately 1912-1918), where the original bolts were cast/forged with a notch under the round head, which corresponded with a similar indent in the steering head - so the bolt could be tightened with just a single spanner on the nut.
Note; I believe the later (post 1917?) type fork also used a similar 'notched' bolt - but was of a longer length (part number 1583d) - sorry but as I have the earlier fork type fitted to both my own Douglas's, I do not have an original 1583d bolt to check against - but expect that if you have the later type forks, this bolt will not fit (however, our engine bolt Item no 0976 might fit - email us on email@example.com for dimension confirmation). Although you may see other photographs of my own Douglas showing it to be of 1919/20 vintage (its frame number is actually 1920) - it has been purposefully fitted with the earlier (pre 1918) forks, as I have built the bike as a 'TT Replica' and the original 1912-14 TT bikes were fitted with the earlier type forks.
We have replicated these original Douglas style bolts - CNC machining them in stainless steel with correct 5/16" x 25tpi Douglas threads, and then a small hole milled under the head to accept a 2.5mm silversteel pin, which is then located with Loctate Retainer fluid (industrial retainer for steel).
The inset picture in the first photograph shows me holding one of our newly manufactured bolt up against the girder fork steering head of the current bike I am restoring. That steering head actually has an original Douglas bolt fitted, but you can see that the head design is the same on our bolts (and obviously does not have the corrosion and wear the original bolt has!)
Sorry these are not cheap - but as well as requiring custom made taps for the threads, the extra effort of milling and fitting silversteel pins make them very labour intensive to produce
There is no reason why - if you are not fussed, that you could replace this type of Douglas bolt with standard modern 5/16" hex head bolts and nuts (and instead use a spanner on both sides when tightening) - but if like me, you would prefer to replicate the original Douglas design and originality - then these do look very nice when fittted