Slight­ly off top­ic, but I thought it would be worth shar­ing my attempt at what might seam the tri­fling prob­lem of secur­ing a bike seat or sad­dle to a bike.

As many cyclists will know, seats or sad­dles can be a real tar­get for thieves — I’ve had at least two stolen. The trou­ble is good sad­dles can get a rea­son­able price on the black mar­ket. If you’re in Lon­don, just pop down to Brick Lane on a Sun­day and you’ll find the cov­et­ed and pricey Brooks sad­dles being flogged for 10s of £s.
To save myself the cost — not to say the uncom­fort­able ride home, sad­dle-less — I’ve been look­ing into ways to bet­ter secure my sad­dle. The crude option is to use some way of lock­ing the sad­dle to the frame, like a small lock or part of a bike chain (see here for ideas). At the more expen­sive end there are ded­i­cat­ed bolts/nuts you can buy with per­son­alised ‘keys’, such as the Sad­dle Lock from Atomic22 (~£29) and options from Pit­Lock (although it’s not clear they have some­thing to bolt the seat to the seat post). These look good, but they’re quite expen­sive and I’ve found if dif­fi­cult to tell which options will fit my bike’s seat-post and saddle.
A solu­tion I’ve come up with is to use a com­bi­na­tion of a gener­ic secu­ri­ty bolt and nut. I’ve found both on an online shop called Secu­ri­ty Safe­ty Prod­ucts.

Locking the seat to the seat post

First I chose a secu­ri­ty bolt to replace the one that attach­es my sad­dle to the seat post. To do that I mea­sured the gauge (width) and length of the cur­rent bolt and then bought the cor­re­spond­ing secu­ri­ty bolt and appro­pri­ate secu­ri­ty screw.

I went for the M8 (8mm thread width) by 50mm long “Pin Hex But­ton head Mach.Screw” (M8x50mm), and the H50 secu­ri­ty screw (the web­site tells you which screw you need).

What you get are 10 bolts (min­i­mum order) and a small screw dri­ver insert with a spe­cial fit­ting. The lat­ter as the web­site explains “”
All I had to do is replace the orig­i­nal bolt that secures your sad­dle to the seat post, with the new secu­ri­ty bolt.

Locking the seat and seat post to the bike frame

To secure the seat post to the bike I found a M8 secu­ri­ty nut that fit the exist­ing seat-post bolt, again on the Secu­ri­ty Safe­ty Prod­ucts site. You can see from the pic­ture on the left that the orig­i­nal nut was a stan­dard well-used bolt.
Also, you need to buy the spe­cif­ic dri­ve sock­et that fits the secu­ri­ty nut — for me, this was a “Remov­able Secu­ri­ty Nut 1/2 dri­ve sock­et KM8R”.  Not sure why, but this is pret­ty expen­sive at £17.99, so it may be worth look­ing for oth­er options here.
The fit­ting is pret­ty straight­for­ward. Use a stan­dard span­ner to unscrew the orig­i­nal nut and then the dri­ve sock­et (attached to a sock­et ratch­et or wrench) to screw on the new bolt.

A few general comments

The down­side with this solu­tion is you can only buy a min­i­mum of 10 bolts and 10 nuts, but at £14.22 and £7.90 per pack (respec­tive­ly), it’s not too painful. Don’t for­get to fac­tor in the cost of the secu­ri­ty screw and dri­ve sock­et though which in my case was £3.58 and £17.99. Also, although Secu­ri­ty Safe­ty Prod­ucts pro­vide a good ser­vice, their postal charges are quite steep.
Of course, noth­ing is fail­safe, and this idea is vul­ner­a­ble to thieves hav­ing the right fit­tings — I don’t think that’s like­ly, though, not until they read this post anyway.
Nat­u­ral­ly, this idea won’t work with all seat and seat post fit­tings. It could work with dif­fer­ent arrange­ments though, just make sure to get the right gauged nuts and bolts and that you’ve got enough room to tight­en them with a screw div­er or spanner.
If you’ve read this far and you think you need a M8 bolt or nut (and live close to East Lon­don) drop me a line. I’ll prob­a­bly have spares of both.

Screw dri­ver with replace­able fitting.
This kind of thing.