One of my bikes uses a torx T40 bolt to clamp the saddle to the top of the seat post.

I am wanting to adjust the position of the saddle slightly by loosening the bolt. But the bolt is done up tightly, and I can't unscrew it using a multi-bit screwdriver. The screwdriver has insufficent leverage to shift the bolt.

Is there a torx T40 size wrench available?

I haven't as yet found such a wrench.

(click on pic)

Torx bits or L-wrenches (look like allan wrenches) are available at any auto parts or hardware stores.

Here are some for sale in NZ even

https://www.sulco.co.nz/Product?Actio...Layout=Printer

without buying a tool, why don't you take a pair of vise-grips and clamp them to your screwdriver and use it like a wrench?

These guys carry Powerbuilt Tools and they make a t40

Store: Bay Engineer Supplies
Address: 140 Hutt Road
Petone, Wellington
Phone: (04) 560 3967

May work as a short term fix, but seems a hassle and offers the oppourtinity to damage the fastener. If the OP intends on keeping the bike for any period of time, it may be well worth while to invest in the t40 bit. Aslo, the jaws of the pliers could mar the shaft of the screw driver if it has a round shaft. If the screw driver is square shafted, an adjustable wrench would indeed work.

Would probably work, depending on the screwdriver handle, but he oughta have a hex wrench-style Torx wrench to carry on rides. For fine-tuning seat position.

Almost every set of 1/4" hex-drive Torx bits I've ever seen includes a T40 and individual bits are widely available. They will fit into any 1/4" hex drive handle or can be used with a 1/4" socket and any ratchet.

Thanks for your comments and links!

The torx T40 seat post screw seems to be done up really tight.

I believe there are torx wrench sets available like Allen key (hex) wrenches, but the local hardware stores I visited do not have them!? Even if the stores had the torx wrench sets, I might not have purchased one because the leverage on these wrenches would probably be very limited due to short 'handle' length (maybe 4" long).

Using Vice Grip on the screwdriver did occur to me, but given the suspect (weakish) construction of the screwdriver, I thought it most likely that the screwdriver would be damaged in the process.

In the end I picked up a 3/8" socket with a torx T40 bit (similar to Craftsman) from a hardware store. And using a 3/8' socket wrench (with a 7 ~ 8" long handle), I was able to unscrew the torx screw and adjust the saddle position!
Although the socket wrench had more leverage, it was still a bit difficult to undo the screw. Whoever tightened the screw in the first place must have jumped up and down on a wrench!?

Probably just corrosion in the threads. Put some anti-seize on the bolt.