How to size a honing steel against your longest blade first, using the stated blade lengths of the Small, Straight Bone-cutting One-piece Keel Boning Knife and The Steel Fish Is Slightly Bent Folding Knife, and what the listings leave unstated.
Size the steel to the longest blade you intend to hone
General sharpening-steel guidance from established sharpening-tool makers holds that a steel should be at least as long as the blade you intend to hone, so the full edge can be drawn along it in one stroke. That guidance is written for those makers' own steels and does not transfer to any particular SEWARD knife, but the sizing logic is simple arithmetic and it answers the question directly: measure your longest blade first, then buy a steel that reaches at least that length.
Your longest blade here is the Small, Straight Bone-cutting One-piece Keel Boning Knife, whose listing states a blade length of 18.2 cm. The Steel Fish Is Slightly Bent Folding Knife states a blade length of 8.5 cm. The difference is 9.7 cm. If you hone both, the boning knife sets the minimum: a steel shorter than 18.2 cm would not cover that edge in a single pass, while the folding knife's 8.5 cm edge would sit comfortably within the same steel.
Those are the listings' stated figures, not measurements that have been checked, and neither listing says where its blade length begins and ends. A sharpened edge can be shorter than the stated blade length, so treat 18.2 cm as the figure to match or exceed rather than an exact edge measurement.
What the two listings do and do not tell you about honing
Neither listing states a sharpening angle, a hardness figure for the boning knife, or a recommended honing routine. The folding knife listing gives hardness figures of 58-60 HRC for the D2 version and 60-61 HRC for the VG10 Damascus version, but a hardness number does not by itself tell you what a steel should be made of, how coarse it should be, or at what angle to hold it. Those are questions for the seller or for the guidance supplied with the steel you buy.
The folding knife listing also does not describe how the blade is locked open. A folding knife needs to be secured before any edge work, and the listing gives no instruction for that. Ask the seller how the knife is held open safely, or follow the maker's guidance for the steel, rather than working from an assumption.
Neither listing states whether the blade or any other part is user-replaceable or serviceable. Where that is missing, it is missing; do not read a honing routine as evidence of either arrangement.
A practical way to decide
Measure the longest blade you actually plan to hone, not the longest knife you own. If that is the boning knife, choose a steel at least 18.2 cm long by the stated figure, and confirm the actual length with the seller, since listings can round or measure differently. If you only ever hone the folding knife, an 8.5 cm blade sets a much lower minimum, and a shorter steel would cover it.
Check the steel's stated length in the same unit as your blade figure before comparing. A steel listed in inches needs converting: 18.2 cm is about 7.2 inches, and 8.5 cm is about 3.3 inches. Ordinary conversion changes how the figure is written, not what it measures.
Finally, ask the seller two things the listings do not settle: where each stated blade length is measured from and to, and what honing guidance applies to the named blade material. A reply that names the measurement points and the method resolves the gap; a reply that only restates the listing does not.
Does the boning knife's 18.2 cm blade length mean I need an 18.2 cm steel?
General guidance says a steel should be at least as long as the blade so the whole edge can be drawn in one stroke. The listing states 18.2 cm as the blade length, not the sharpened edge length, and does not say where the measurement runs. Use 18.2 cm as the figure to match or exceed, and confirm the actual edge length with the seller.
Can one steel serve both knives?
By the stated figures, yes, if it is at least 18.2 cm long: the folding knife's stated 8.5 cm blade is shorter and would fit within the same steel. That is arithmetic on stated lengths, not a statement about how either edge responds to honing.
Do the listings give a honing angle?
No. Neither listing states a sharpening or honing angle, and the boning knife listing gives no hardness figure. Ask the seller or follow the guidance supplied with the steel rather than assuming an angle.
